Orthosilicates [2 ed.] 0939950057, 0939950138

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REVIEWS In MINERALOGY Volume

5

ORTHOSILICATES SECOND EDITION PAUL H. RISSE, Editor The Authors Friedrich

Liebau

Mineralogisch-Petrographisches Museum der Universitat Kiel Olshausenstrasse 40-60 2300 Kiel, West Germany

Institut

und

E. Patrick Meagher Department University Vancouver,

J. Alexander

of Geological Sciences of British Columbia B.C. Canada V6T 2B4

Speer

Paul H. Ribbe Department of Geological Sciences Virginia Polytechnic Institute & State University Blacksburg, Virginia 24061

Gordon E. Brown, Jr. Geology Department Stanford University Stanford, California

Series Editor Virginia

94305

Paul H. Ribbe

Department of Geological Sciences Polytechnic Institute and State University Blacksburg, Virginia 24061

MINERALOGICAL

SOCIETY

OF AMERICA

COPYRIGHT 1982 Mineralogical Society of America PRINTED BY BookCrafters, Inc. Chelsea, Michigan 48118

REVIEWS IN MINERALOGY (Formerly: SHORT COURSE NOTES) ISSN 0275-0279

VOLUME 5: First Edition

ORTHOSILICATES

(1980) ISBN 0-939950-05-7

Second Edition (1982) ISBN 0-939950-13-8

Additional copies of this volume as well as those listed below may be obtained at moderate cost from Mineralogical Society of America 2000 Florida Avenue, NW Washington, D.C. 20009 No.of Vol.

~

1

SULFIDE MINERALOGY.

2

FELDSPAR MINERALOGY.

3

OXIDE MINERALS.

4

MINERALOGY and GEOLOGY of NATURAL ZEOLITES. F.A. Mumpton, Editor (1977)

232

5

ORTHOSILICATES.

450

6

MARINE MINERALS.

7

PYROXENES.

C.T. Prewitt, Editor (1980)

525

8

KINETICS of GEOCHEMICAL PROCESSES. A.C. Lasaga and R.J. Kirkpatrick, Editors (1981)

391

AMPHIBOLES and Other Hydrous Pyriboles - Mineralogy. D.R. Veblen, Editor (1981)

372

9A

P.H. Ribbe, Editor (1974)

284

P.H. Ribbe, Editor (1975; revised 1982) ~350

Douglas Rumble III, Editor (1976)

P.H. Ribbe, Editor (1980; revised 1982) R.G. Burns, Editor (1979)

AMPHIBOLES: Petrology and Experimental Phase Relations. D.R. Veblen and P.H. Ribbe, Editors (1982) 10 CHARACTERIZATION of METAMORPHISM through MINERAL EQUILIBRIA J.M. Ferry, Editor (1982)

502

380

9B

~

390 397

ORTHOSI LICATES

SECOND EDITON

FOREWORD The Mineralogical

Society of America sponsored its first Short Course in con-

junction with its annual meetings in November 1974.

Contributions of the lecturers

were published in a paperback book entitled Sulfide Mineralogy.

In 1975 the Short

Course and book were entitled Feldspar Mineralogy, in 1976 Oxide Minerals, and in

1977 Mineralogy and Geology of Natural Zeolites.

In 1978 the Short Course Commit-

tee decided to forego activities because the annual meeting of the M.S.A. was held together with the Mineralogical Association of Canada, who sponsored a Short Course in Uranium Deposits and published a book by the same title.

A number of mineralo-

gists expressed regret at the potential loss of momentum in M.S.A.'s production of this series and encouraged several authors of this book to press on with their idea of publishing Volume 5 -- Orthosilicates.

Work was begun in 1978; however, without

the pressure of a deadline associated with presenting the material to students of a short course at the annual meeting, procrastination

set in and the first edition of

this volume was not completed until September 1980 (with the exception of Chapters 1 and 2 which were submitted in their present form in 1978).

In the meantime Vol-

ume 6, Marine Minerals, appeared in time for the annual meeting of the Society and a Short Course in San Diego in November 1979. In 1980 the Council of the M.S.A. changed the name of the published volumes from "SHORT COURSE NOTES" to "REVIEWS in MINERALOGY"

in order to more aptly describe

the material contained in this now highly successful series.

The First Edition of

Orthosilicates was the first volume to appear under the "REVIEWS" banner.

Subse-

quently Volumes 7, 8, 9A, 9B, and 10 have appeared (see p. ii); Volume 2 is being totally revised, Volume 11 is planned to be a monograph on Fluid Inclusions, and Volume 12 will be entitled Carbonates. This is the Second Edition of Orthosilicates.

It contains an updating and min-

or revisions of Chapters 3 through 10 (only) and two new chapters originally intended for the First Edition.

Chapter 12 contains very brief descriptions of the para-

genesis and crystal chemistry of many orthosilicates in the Preface (p. iv). listed alphabetically,

that fit the description stated

It may be used as an index, because all orthosilicates including those discussed in Chapters 2 through 11.

are

Minerals

which have individual Si04 groups polymerized to other cations (Be, B, AI, Zn, etc.) in tetrahedral coordination are described in Chapter 13, together with some whose structures are unknown but are thought to be orthosilicates classified as orthosilicates

and some which have been

in the past but are now known not to be such. Paul H. Ribbe

Series Editor Blacksburg, VA iii

ACKNOWLEDGMENTS The editors of journals and publishers of books from which figures have been reproduced are gratefully acknowledged for their cooperation. Ramonda Haycocks and Margie Strickler patiently and skillfully typed the manuscript, and Alex Speer shared proof-reading responsibilities with the editor. The Department of Geological Sciences at Virginia Polytechnic Institute and State University provided the facilities at which much of the manuscript writing and preparation were undertaken.

The editor acknowledges the financial support of

the National Science Foundation (Grant EAR 77-23114 to G.V. Gibbs and PHR) during the four years in which this book has been in progress.

PREFACE The intent of this volume is to emphasize the crystal chemistry and related physical properties of the major rock-forming orthosilicates.

Though in some

chapters more attention is given to phase equilibria and paragenesis than in others, these are for the most part cursorily treated with references to the more important papers and to review articles (also see Deer, Howie and Zussman,

1962, Rock-forming MineraZs, VoZ. 1, Ortho- and Ring SiZicates). Some confusion will inevitably result from the definition of the term used as the title for this volume.

In Chapter 1 Liebau (p. 14) says that

"silicates

containing [Si04] groups should be called monosiZicates rather than orthosilicates or nesosilicates." The editor chose not to adopt Liebau's terminology for the title, because monosiZicate is not yet widely accepted (although it might well be).

To set manageable boundaries for the scope of the First Edi-

tion of OrthosiZicates, an editorial option was exercised in rejecting as "orthosilicates" those minerals with both [Si0 J tetrahedra and [Si 0 ] groups (zoi4 2 7 site, epidote, vesuvianite, etc.), as well as those with [Si0 ] tetrahedra that 4 are polymerized to other tetrahedra by sharing corners with [Be0 ], [B0 ], 4 4 [A104], [Zn04], etc. However, as mentioned in the Foreword, Chapter 13 has been added to the Second Edition to correct for the latter omission. Also, Chapter 12 serves as an alphabetical index for the previous ten chapters and includes most of the more obscure minerals that fit our restricted definition of orthosilicate.

iv

ORTHOSILICATES TABLE of CONTENTS

Page

Copyright and Additional Copies

ii

Foreword

iii

Acknowledgments

CHAPTER 1.

and Preface

iv

CLASSIFICATION OF SILICATES

F. Liebau

...............

INTRODUCTION

CRYSTAL CHEMICAL CLASSIFICATION

1

OF SILICATE ANIONS

2

Treatment of tetrahedrally coordinated cations Dimensionality of silicate anions Unbranched, branched and hybrid silicate anions Multiplicity of silicate anions Periodicity of silicate anions Structural formulae of silicate anions Nomenclature of silicates CRYSTAL CHEMICAL CLASSIFICATION

OF SILICATES

14

................

Mixed Jpion silicates Further subdivision .o f silicates Shortcomings of the crystal chemical classification OTHER CLASSIFICATIONS

2 3 3 6 7 9

of silicates

OF SILICATES

COMPARISON OF DIFFERENT ACKNOWLEDGMENT

CHAPTER 2.

15 16 16 19

Kostov's classification Zoltai's classification

REFERENCES:

15

19 20

SILICATE CLASSIFICATIONS

22

SILICATE CLASSIFICATION

24

. • . • •

24

SILICATE GARNETS

E.P. Heagher

INTRODUCTION

25

CRYSTAL STRUCTURE.

25

GARNET CHEMISTRY

.

27

Titaniwn Zirconiwn Phosphorus-sodiwn Yttriwn Vanadiwn Tin

32 32 33 33

33 33

RELATION BETWEEN PHYSICAL PROPERTIES AND CHEMISTRY

33

CRYSTAL CHEMISTRY ..•••.....

35

Structural response to chemical variations Si04 tetrahedron Y06 octahedron XOa triangular dodecahedron Composite structure Calculation of cell parameter and atomic Structural response to elevated temperatures Structural response to elevated pressures v

36 36 38

41 41 coordinates

42

44 46

Page

CHAPTER

2, ccntinued

GARNET-HYDROGARNET

SERIES X3Y2(Si04)3_p(H404)p

(0 ~ p ~ 3)

Hydrogrossular Crystal structure of CaJAl2(H404)3 Hydroandradite Hydrospessartine Cation ordering COMPOSITIONAL

ZONING IN GARNETS.

CHAPTER

GARNETS

3.

49

51 52 52 54 55

Metamorphic garnets Igneous, hydrothermal garnets REFERENCES:

48

55 57

...•.....•

58

ZIRCON

J.A. Speer

INTRODUCTION

67

CRYSTAL STRUCTURE.

67

69

The structure of zircon polymorphism

71

AB04

71

CHEMISTRY ...•..••.. ZrSi04-HfSi04 solid solutions ZrSi04-YP04-REEP04 solid solutions Uranium, thorium and radiogenic elements Other substituents Water

73 74 76

78 78 80

ZONING ..

80 81 82 82

Chemical zoning Growth zoning Passive zoning Outgrowths and overgrowths Sector zoning MORPHOLOGY

84 84

. • . •

Morphology as a petrogenetic indicator Twinning Cleavage Optical properties Color Density Lattice parameters Hardness and elastic properties Thermal properties Luminescence

EXPERIMENTAL

STUDIES

88 89 90

91 91 94 95

96

100

.

100 101

GEOCHRONOLOGY.

Isotopic U,Th-Pb method Isotopic Xe-Xe method Isotopic Sm-Nd method Chemical methods; Fission track method Thermolwninescence dating; Degree of metamictization REFERENCES:

88

96

METAMICTIZATION •..

ALTERATION

84

101 102 103 103 104

106

ZIRCON ..... vi

Page

CHAPTER 4.

THE ACTINIDE ORTHOSILICATES

INTRODUCTION:

J .A.

115

CRYSTAL STRUCTURE. Thorite Coffinite Huttonite CHEMISTRY ...

• ....•..••.•.......

Thorite Substituents Substituents Water Halogens Huttonite Coffinite PHYSICAL PROPERTIES.

"

for thoriwn for silicon

• • . . • . • • . . . • • • • • • . . • • . • . • ..

Metamict actinide orthosilicates

Coffinite analysis;

CHAPTER 5.

Brabantite

119 119 121 122 123 123 124 125

127 128 132

The ACTINIDE ORTHOSILICATES

TITANITE

115 117 117 119

126

GEOCHRONOLOGY ...•• SYNTHESIS, PHASE STABILITY AND PHASE ASSEMBLAGES OF ACTINIDE ORTHOSILICATES. REFERENCES:

Speer 113

OCCURRENCES

133

P.H.

(SPHEN~

Ribbe

INTRODUCTION

137

CRYSTAL STRUCTURES

137

The structure of P2l/a synthetic CaTiO[Si041 The P2l/a + A2/a transformation at 220°C The A2/a structure of malayaite at 25°C Predicted structures at high pressures and high temperatures Nonsilicates isostructural with titanite and ma1ayaite CRYSTAL CHEMISTRY.

142

Immiscibility in the system CaTiO[Si041 - CaSnO[Si041 Stoichiometry Electrostatic charge balance and chemical substituents Summary of substituents in titanite The ?-coordinated Ca polyhedron The underbonded 0(1) site The Si site The Ti octahedron Lattice parameters Metamict titanites Domain textures PHYSICAL PROPERTIES AND TWINNING

142 142 143 143 143 144 144 145 145 146 147 148

Electric properties Optical properties Cleavage, hardness, density Thermal expansion Twinning Growth twins Mechanical twins REFERENCES:

138 139 140 141 141

148 148 149 149 150 150 150

TITANITE .•.

152 vii

CHAPTER

6.

CHLORITOID

P.H. Ribbe

INTRODUCTION

155

CRYSTAL STRUCTURES

157

Monoclinic chloritoid Possible polytypes of ch10ritoid Triclinic chloritoid, 1Tc STACKING DISORDER IN CHLORITOID:

157 159 159

POLYTYPISM OR HOMOLOGY?

160

CRYSTAL CHEMISTRY, PHYSICAL PROPERTIES AND TWINNING •...

163

Chemical variation Specific gravity, hardness Cleavage and curved basal plates Optical properties Twinning

163 164 165 165 166

DEHYDRATION AND STABILITY.

167

Topotactic dehydration-oxidation Stability REFERENCES:

167 168

CHLORITOID ..

169

STAUROLITE

P.H. Ribbe

CHAPTER 7. INTRODUCTION

171

CRYSTAL STRUCTURE.

173

STACKING FAULTS, TOPOTAXY, AND.ANTI-PHASE DOMAINS.

175

MORPHOLOGY, CLEAVAGE AND SECTOR ZONING

176

COMPOSITION ..

178

Iron Zinc Hydroxyl

180 181 181

LATTICE PARAMETERS

182

OPTICAL AND OTHER PHYSICAL PROPERTIES.

184

TWINNING ..

185

REFERENCES:

STAUROLITE.

CHAPTER 8.

KYANITE,

186

ANDALUSITE

and Other Aluminum Silicates

P.H. Ribbe

INTRODUCTION Phase equilibria (Al,Si)IV order/disorder in sillimanite CRYSTAL STRUCTURES AND RELATED PHYSICAL PROPERTIES . . . . . . . . . . . •. Kyanite, AliIO[Si041

189 189 190 191 194

Differentialhardness and cleavage 1Winning, deformationmechanisms,and anti-phasedomain boundaries Thermal expansion Andalusite, AlVIAlVO[Si041

195 195 196 196

Thermal expansionand compressibility Deformation Sillimanite, AlVI[A1IVSiIV051

198 198 199

Thermal expansionand compressibility Fibrolite Mul1ite, AlVI[(A1l+2xSil_2x)IV05_x]

199 200 200

viii

CHAPTER 8,

Page

continued

COMPOSITIONAL VARIATIONS AND RELATED PHYSICAL PROPERTIES Naturally-occurring aluminum silicates Anda1usite, viridine and kanonaite Sillimanite Natural kyanites Synthetic transition metal-bearing kyanites, REFERENCES:

CHAPTER 9.

• . . . . • • . . .

203 203 205 208 209

(A12_xM~+)VIO[Si041

ALUMINUM SILICATE POLYMORPHS AND MULLITE

TOPAZ

210

212

P.H. Ribbe

INTRODUCTION

215

CRYSTAL STRUCTURE.

215

The structure of orthorhombic topaz "Anomalous" topazes The structure of tric1inic topaz Twinning, intergrowths and dislocations PHYSICAL PROPERTIES; FLUORINE DETERMINATIVE METHODS. Habit, cleavage, thermal expansion and density Optical and electrical properties Color

Refractive indices and 2V: orthorhombic topaz Optic orientation and 2V: monoclinic and triclinic topaz Piezoelectricity and pyroelectricity Lattice parameters Fluorine analysis

CHAPTER 10.

222 222 223 223 225 225 226 226 227

TOPAZ-VAPOR EQUILIBRIA AND THERMODYNAMIC REFERENCES:

215 217 219 222

PROPERTIES.

TOPAZ ..

227 229

THE HUHITE SERIES AND Mn-ANALOGS

P.H. Ribbe

INTRODUCTION

231

CHEMISTRY •.

232

Substituents in octahedral sites Substituents in tetrahedral sites Stoichiometry CRYSTAL STRUCTURES

235 236 237

.

239

Structural homology; octahedral chains Space groups Individual structures

Norbergite Chondrodite Hwnite Clinohwnite Bonding in the humite minerals CRYSTAL CHEMISTRY.

239 241 241 242 243 244 245 246 248

Titanium Iron Manganese and calcium Fluorine and hydroxyl

Effective radii of F and OH Unit cell volwnes and ionic radii

248 251 252 255 256 258

PHYSICAL PROPERTIES ...

259

Optical properties Specific gravity

259 261 ix

CHAPTER 10,

PHYSICAL PROPERTIES,

Thermal breakdown TWINNING

Page

continued

reactions and the effects of annealing

261

. .

262

HUMITE STRUCTURES AS ANION STUFFED CATION ARRAYS

264

FAULTED STRUCTURES,

266

INTERGROWTHS,

AND SUPERSTRUCTURES.

Superstructures Jerrygibbsite and Leucophoenicite APPENDIX:

Previously

REFERENCES:

unpublished

267 268

microprobe

analyses of the humite minerals

THE HUMITE SERIES AND Mn-ANALOGS ...

CHAPTER 11. INTRODUCTION

OLIVINES AND SILICATE SPINELS

269 272

G.E. Brown, Jr.

.

275

THE OLIVINE AND SPINEL STRUCTURE TYPES

276

COMPOSITIONAL

282

RANGE OF OLIVINES AND SILICATE SPINELS

LOW PRESSURE PHASE RELATIONS NOMENCLATURE

AND COMPOSITIONAL

. . . . . . . . VARIATIONS

OF THE NATURAL OLIVINES.

Major element chemistry

Forsterite-fayalite series Tephroite-fayalite-forsterite series Monticellite Minor element chemistry

Calciwn Manganese Nickel Chromium

Alwninwn Ferric iron Alkalis Water Uraniwn and the lanthanides Titaniwn Defects Inclusions

in olivine

GEOLOGIC OCCURRENCE ALTERATION

OF OLIVINES.

303 303 303 306 307

STRUCTURE AND BONDING IN OLIVINES.

309

response to compositional

changes

Octahedral distortions Computer simulation of the olivine structure Structural

290 290 290 292 292 292 295 295 296 296 297 297 297 298 298 298 298

301

OF OLIVINES.

Color Optical properties Density Unit cell parameters

Structural

289

299

AND OXIDATION OF OLIVINES

PHYSICAL PROPERTIES

284

response to temperature

change

Unit cell expansion Structural expansion Structural view of olivine melting Ca2Si04 polymorphism Structural response to pressure changes Summary of P, T, X effects on the olivine structure Bonding in olivines x

309 316 318 320 321 321 321 324 325 328 329

Page

CHAPTER 11, continued 334

INTRACRYSTALLINE CATION PARTITIONING IN OLIVINES • . • . • . .

Observations from X-ray and spectroscopic studies Factors affecting octahedral cation distributions in olivines Comparison of intracrystalline cation partitioning in olivines and orthopyroxenes INTERCRYSTALLINE CATION PARTITIONING BETWEEN OLIVINE AND OTHER SOLID PHASES. Olivine Olivine Olivine Olivine Olivine Summary

-

335 335 340 342 342 344 345 346 347 347

orthopyroxene clinopyroxene garnet spinel sulfide

347

MELT GROWTH OF OLIVINES AND OLIVINE - MELT CATION PARTITIONING

348 349 350

The nature of olivine composition melts Melt growth of olivines Element partitioning between olivine and melt THE OLIVINE

+

353

SPINEL TRANSITION ..•..•.••.

High pressure phase relations in the system Mg2Si04-Fe2Si04 Structures of the 8-Mg2Si04 and y-Mg2Si04 po1ymorphs Structural rationalization of the stabilities of the a-, 8-, and y-polymorphs Geophysical consequences of the olivine + (y,8)-spinel transformation

353 354 355 357 357

TRANSPORT PROPERTIES OF OLIVINES

357 358 359 359

Cation diffusion Conductivity Radiative heat transfer Lattice thermal conductivity ELECTRICAL AND MECHANICAL PROPERTIES OF OLIVINES

359

REFERENCES:

365

CHAPTER

12.

OLIVINES AND SILICATE SPINELS ...

HISCELLANEOUS

ORTHOSILICATES

J.A. Speer & P.H. Ribbe

INTRODUCTION.

393

This chapter contains brief descriptions of minerals in which [Si04] groups are not polymerized to other [Si041 groups, nor are they polymerized to other tetrahedral radicals containing such cations as Be, B, Al or Zn. In addition, this may be used as an INDEX to Chapters 2-11, since all mineral names of orthosilicates as defined in the Preface (p. iv) are listed here alphabetically, with reference to the place they are described in the text.

CHAPTER

13.

INTRODUCTION.

ORTHOSILICATES with Si04 Polymerized to Other Tetrahedral Po1yanions J.A. Speer

& P.H. Ribbe

. . . . . . . . . .

429

This chapter contains an alphabetical listing of all the silicates the authors could locate in major compendia which have been classified as ortho-, neso-, or monosilicates but in which "isolated" [Si04] groups are polymerized by corner-sharing with other tetrahedral groups, such as [BeO4], [BO4], [AIO4], and [ZnO4 J • Included are some minerals whose structures are unknown but are suspected to be orthosilicates.

xi

This page is blank.

Chapter 1 F. Liebau

of SILICATES

CLASSIFICATION

INTRODUCTION Silicates

form the largest

to deal efficiently

with

sary to put them in a suitable indicated

by the word

but it does fulfill

a purpose.

fulfills

Dealing with classification

as chemical (covalent,

chemistry

a very suitable

of silicates

structure

purposes, is

a

directly

of the chemical

bonds

Since the atomic struc-

by the chemical

properties

that is based on atomic

the chemistry

requires

and the chemistry

may be applied

in the silicates.

is controlled

such a way that it reflects

As is

The best classification

and/or as character

a classification

them.

has no end in itself,

purpose best.

In this regard chemistry

composition

In order it is neces-

there are different

classifications.

the structural

ture of a substance

of its

structure

of the substance

in

would be

one.

It is common practice minerals

Because

the particular

ionic) occurring

constituents,

classification

based on both the atomic

of the silicates.

of silicates

order, i.e., to classify

'suitable,'

there will be different that which

single group of minerals.

the large variety

according

to classify

silicates

as well as other

to the kinds of their coordination

the way these polyhedra

are linked.

°,

polyhedra

and

A silicate may be represented

as M',M':,M'::, ..•Si for there is a wide variety of [MO ] polyrr r st n hedra in silicates. By contrast, [Si04] tetrahedra and [Si0 ] 6 octahedra are the only [SiOn] polyhedra known to exist in silicates. This makes

[SiOn] polyhedra

cation of silicates.

the most suitable

Classification

for a basic classifi-

schemes based on the kind and

degree of polymerization by Bragg

of [Si04] tetrahedra have been developed (1930) and Naray-Szab6 (1930) and extended by Zoltai (1960)

and Liebau

(1962, 1972, 1978).

tion of the present silicates discussion

In the following

state of this crystal

is given; a more detailed of the crystal

(Liebau, 1980).

chemical

a concise

chemical

description interpretation

descrip-

classification

together

with a

is in preparation

of

CRYSTAL Silicon

CHEMICAL

CLASSIFICATION

is either

or octahedrally

tetrahedrally

by six.

Although

OF SILICATE coordinated

the number

ANIONS

by four oxygen

of phases

[Si0 ] groups is still small (ca. 30) it increases 6 pressure methods become available. In principle, or share corners, forces between

as new high-

[Si0 ] and [Si06] groups can either be isolated 4 edges or faces (Table 1). Due to strong repulsive

the silicon

(Weiss and Weiss,

atoms

containing

atoms only one example

1954) -- with edge-sharing

-- fibrous

tetrahedra

Si02

and none with

Table 1. Very broad division of silicate anions; one or more example known, +; no examples, o. [Si04] tetrahedra

[Si06] octahedra

isolated

+

+

corner-shared

+

+

edge-shared

+

+

face-shared

0

0

face-sharing

[Si0 ] has been observed. By contrast, for [Si0 ] octa4 6 edge-sharing (as in stishovite) seems to be as common as corner-

hedra

sharing.

Face-sharing

has not been observed

in either of the two

kinds of [SiO ] polyhedra. While the large number of silicates conn taining [Si0 ] tetrahedra require further subdivision, it is prema4 ture to further subdivide phases with [Si06] octahedra. Treatment

of Tetrahed~ally

Whenever, of silicon

Coordinated

under any conditions,

by cations

Cations there is isomorphous

M in a tetrahedrally

coordinated

replacement

site

T,

the

corresponding

[T0 ] tetrahedron is regarded to be part of the silicate 4 Such replacement is most common for A13+ but is also observed 3+ 4+ .4+ 3+ 5+ 3+ 2+ for Fe ,Ge ,T~ ,B ,P ,Ga ,and Be . If a tetrahedrally

anion.

coordinated

cation M does not replace

and at temperatures silicate,

and pressures

its [M0 ] tetrahedra 4

Si, not even in small amounts

near to the stability

are not regarded

cate anion. 2

limits

of the

as part of the sili-

According silicate, while

to this convention

K[AlSi30S1,

petalite

Dimensionality

even in completely

ordered

maximum

microcline,

of Si/Al or Si/Li is achieved. of Silicate

Anions

If a finite number

of [T04] tetrahedra anion is finite or, in other words,

sions.

Condensation

to one-dimensionally

of an infinite infinite

number

chains

or to three-dimensionally

Branched

An isolated

and Hybrid

is linked infinite

the resulting in zero dimen-

of tetrahedra

leads either

or to two-dimensionally

infinite

ality of such anions is, therefore, Unbranched,

is a framework

of formula Li[41Al[4] [Si 0 ] 4 l0 into a new phase before statistical redistribu-

complex

layers

feldspar

is a layer silicate

since it transforms tion (disorder)

potassium

said to be d

Silicate

=

infinite

The dimension-

frameworks.

0, 1, 2, or 3.

Anions

[T04] group that does not share a corner with another

[T04] group is called ing number of corners

a singular

or single

tetrahedron.

With increas-

[T0 ] groups the tetrahedra 4 are called primary, secondary, tertiary and quaternary [T0 ] tetrahedra. 4 Silicate anions containing only primary and secondary [T0 ] tetrahedra 4 are called linear silicate anions. They are either multiple tetrahedra or single linear

chains

shared with other

or single rings.

Figure

1 presents

several

typical

anions.

~ a

b

c FIgure 1. anions.

Several fundamental linear

(a) Double tetrahednm [SI20 ]. 7 (b) Triple tetrahed"", [SI 0 ]. 3 l0 (c) Linear single chain {.).J [SI20 ]. 6 (d) Single ring {el[Si 0 ]. 4 12

d

3

~

b

a

e

d Figure 2.

Several

fundamental branched silIcate

Open branched triple

tetrahedron

(b)

Open branched vierer

ring

(c)

Open branched secnser

(a)

(oB,e)[

6

anIons.

[SiS016] of zunyUe. of eakerite.

{oB,e1[4si60lS1

ring

S1lS0S41 of tienshanlte.

(d)

Open branched zweier

single

chain (~ ~

~~ ~ ~

f>~ f>~

~ ~ ~

b

FIgure S.

a 4. n }- 4. 1 I~ H H J\ I~~ ~, ~

~

~

I : }-~ I ~,~

.......

~

c

4~

~

~

e

d

f

h

9

Unbranched double chaIn sIlIcate anIons.

(a) Unbranched einer double chaIn of slllimanit~A1{U,2J.}[l(SiAl)051. (b) Unbranched zweier double chain of amphibole, caZMgs{U,2J.J[2Si40ll)2(OH)2' (c) Unbranched zweier double chain of synthetIc Li {U,2J.J[2(SiGe3)O l. 4 lO (d) Unbranched dreier double chaIn of xonotlIte, ca6{U,2J.J[3S160l7) (OH)2' (e) Unbranched dreier double chaIn predicted In devltrlte, NSZCa3{U,2J.J[3Si6ol61. (f) Unbranched dreler double chaIn of synthetic Na Be2H{U,2J.} [3Si 0 1 (OH). 2 6 ls (g) Unbranched vierer double chaIn of narsarsuklte, Na4(TI0)Z{U,2J.}[4S1S0Z01. (h) Unbranched fUnfer double chain of Ineslte, (Mn,Ca)9{U,2J.J[5Sil002S1 (OH)2·sH20. 2+

3+

I

6

(i) Unbranched secnser double chaIn of tuhualite, (Na,K)2Fe2 Fe2 {U,2®}[ Sil20301·H20 .

... ,~'" ..

.,,~~ ... ::;...;;(1. "''''' ~

,~~

~

,~,,-f

~ ~

;r~ .. a

FIgure 9.

}.~ .;;(1. }.~ .;;(1. }.~ .;;(1. }.~

garnet>

pyroxene

40

~ olivine

associated Cr3+ de-

(Burns, 1976).

XOs triangular

dodecahedron.

The major

elements

occupying

the

eight coordinated triangular dodecahedral site in silicate garnets are 2 Mg, Fe +, Mn and Ca. Zemann (1962) proposed the permissible range of rX in the natural maximum

garnets

permissible

accompanying

For synthetic

labeled

and Smith, 1965).

in the neighboring

The average

x-o

increases increases

dependent

A

from 0.53

A

by 0.03

on .

garnet

is significantly

constraints

octahedra

related

to

(Zemann,

1962; Gibbs

, appears

to increase

garnets;

however,

For example,

in grossular

which are

In all silicate

to 0.64

(Novak and Gibbs, 1971;

the upper

A.

1.5

distances

distance

distance,

with in the AI-silicate

is also strongly

Novak and Gibbs

is increased,

to be the result of geometric

Y-O and 0-0 distances

linearly

(Fig. 1).

to date, the X(2)-0(4)

and appears

x-o

that the

on the size of the

garnets

to approximately

non-equivalent

and X(2)-0(4)

refined

however,

is dependent

that as the size of the Y-cation

X(1)-0(4)

structures

It appears,

silicate

limit for rX can be increased

There are two symmetry

longer

A.

size of the X-cation

Y-cations.

(1971) proposed allowed

to be 0.8-1.1

cf.

the value

in the Ca-garnets

A

in andradite,

Higgins

as

and Ribbe, 1977,

Fig. 2). Among stabilization

energy.

Burns

(1970) estimates

pyrope-almandine

series ranges 2 Of the Fe +-containing

almlOO' mantle

rocks,

M2-site

minerals

the CFSE decreases

structure.

of the specific

cal variations. exists between

as:

that the CFSE in the

associated

garnet

It is apparent,

adjacent

polyhedra.

strongly

dependent

octahedron

In the preceding

polyhedr~

the geometry

to 11.7 kcal in l with garnet in upper

(8-coordinated)

sections

have been discussed however,

> pyroxene

For example,

relative

(1962).

re-

to chemi-

and the chemistry

of

the size and shape of an octahedron occupying

occupying

is

the

the neighbor-

sites.

One of the first to investigate was Zemann

the geometric

not only on the for the cations

dodecahedral

with the

that a strong interdependence

of a given polyhedron

but also on the radius of the cations

ing triangular

field

from 12.4 kcal in alm

Ml ~ olivine Ml and M2, which is consistent enrichment of Fe2+ in the garnets (Burns, 1976).

Composite

garnets

a crystal

> pyroxene

relative

lations

only Fe2+ experiences

the common X-cations

these interdependent

Zemann was curious

41

relations

about the geometric

in

constraints

operative

in pyrope and grossular

rence of an undistorted

Si0

which prohibit

the occur-

tetrahedron

and Al06 octahedron. Using of appropriate dimensions for pyrope and

4 ideal Si04 and Al06 polyhedra grossular, he computed the resulting

interatomic

distances

in the Mg0

8 and Ca08 polyhedra and found an abnormally short unshared 0-0 edge of 2.44A present in each. Upon expanding the distance to 2.75 A (which Zemann felt was a minimum X08 polyhedron),

distortion

A more powerful tween various

allowable

the Distance

Least

1969).

this program,

least-squares parameters

adjustment

and calculated of aluminum

silicate

culations

indicate

of independent

that geometric interactions

than the unshared

edge in the Y

of can be reproduced

of cell parameter

have been computed

(1971) with which the mean radius

56 silicate

analysis

=

in parentheses

the last place quoted. comm.) extended natural

and synthetic

1.61(4)

in a silicate

analysis

Regression

a, knowing

garnet.

The mul-

(1971) was completed

for

relation:

standard

deviation

by Novak and Colville

to include

and yielded

42

(Fig. 8)

(1964) and Novak and Gibbs

+ 1.89(8)

regression

the observed

edges

the unit cell parameter,

A subsequent

garnets

edge is shorter

In addition,

refer to one estimated

the multiple

play an impor-

and atomic coordinates.

by Novak and Gibbs

+

polyhedra

octahedral

and led to the following 9.04(2)

(1975) to evaluof r ' The calX about by cation-

6 with this method.

by McConnell

one can estimate

garnets

a The numbers

Al0

of the X- and Y-cations

tiple regression

values

tetrahedral

Al garnets.

prescribed

(DLS) investigation

brought

in adjacent

and a

and unit cell

between

by Meagher

constraints

of shared and unshared

Calculation equations

=

(Meier and Villiger,

least-squares

to increasing

be-

in the form of

atomic parameters

that the shared

resulted.

are prescribed,

the difference

A distance

tant role in determining

trend in lengths

program

distances

garnets was undertaken

anion and anion-anion

as a function

(DLS) computer

of the structure

and octahedron

edge of an

the interrelationships

is now available

interatomic

to minimize

distances.

ate the response

and angles

Squares

is computed,

for the unshared

in the tetrahedron

means of determining

bond lengths

With

distance

in (pers.

for over 1100

the relation:

1.00

.90

.80

05 ~ -c-

.70

I

Fe C'

OOf AI .50

Mg Fe .80

Mn

.90

Ca 1.00

1.10

(rV

1.20

1.30

1.40

1.50

(.A.)

Figure 9. The proposed "s t ab Le" silicate garnets for which compatible combinations of and Occur. Effective ionic radii of some commonX- and Y-cations (Shannon and Prewitt, 1969) are shown. The radius of Fe is for 2+ along and 3+ along ' After Novak and Gibbs (1971).

a

=

8.44 + 1.71(1)

In both equations

the effective

are used with the exception and Colville Novak

+ 1.78(1)

+ 2.17(1)

Z

ionic radii of Shannon and Prewitt

of some rare-earth

(1969)

ionic radii in the Novak

investigation.

and Gibbs

(1971) completed

sis of the oxygen atomic coordinates from their nine silicate

a multiple versus

linear regression

.and

garnet refinements.

analy-

using the data

The following

equations

are obtained:

x

=

0.0059(5)

+

y

= =

0.0505(4)

- 0.023(2)

+ 0.037

0.6431(7)

- 0.009(3)

z

0.022(2)

Using the above relations atomic

coordinates,

the crystal

garnet

can be approximated

occupy

special

positions

to compute structure

+ +

0.014

0.034

the cell parameter of a hypothetical

since the X- and y-cations, in the space group Ia3d. 43

and oxygen silicate

as well as Si,

Novak and Gibbs

(1971)

used this technique, net refinements, of silicate

garnets.

which a "stable" guidelines distance, culated

silicate

the 0-0 distance

garnets

Figure 9 along with and y-cations.

allowed

+

a series of guidelines In general,

octahedral

and triangular rO radii sums.

Si-O

edge and the calsites com-

Accordingly,

an area was

ry plot within which the crystal-chemically

occur.

This type of plot is illustrated

the Shannon-Prewitt

of this diagram

pear to be compatible

these

dodecahedral

in

radii for the more common x-

One can see that the common silicate

the lower portion

from gar-

exist in the chemistry

length of the calculated

in the unshared

rO and rX

out on an rX Versus

stable silicate

data obtained

might

garnet could not exceed.

the maximum

size of the octahedral

+

chemical

what limitations

To do this they proposed

included

pared to the ry mapped

along with crystal

to estimate

garnets plot toward

and much larger X- and Y-cations

ap-

with the garnet structure.

Structural response to elevated temperatures To date, structure have been completed spessartine

refinements

for pyrope

and andradite

with increasing no significant

of garnets

and grossular

(Rakai, 1975).

temperature

(Meagher,

in these four garnets

Y-O distances,

temperatures

1975) and for

The structural

change in the Si-O interatomic

the mean octahedral

at elevated

adjustments

are similar

distance

in that

occurs whereas

, and distances

increase

in a simple linear manner. Although

increased

temperature

does not significantly

of the Si04 tetrahedron, the tetrahedron role in the thermal expansion of garnets.

change the

dimension

plays more than a

passive

In pyrope and spes-

sartine,

the tetrahedron

temperature

rotates

(as was illustrated

the effect of increasing

=

unit cell.

In the Y

increasing

temperature,

spessartine

of y with increasing

Al garnets dy/dT,

tine, as the tetrahedron the shared Al06 octahedral

the rate of tetrahedral

is highest

in pyrope,

rotation

intermediate

with in

iil grossular.

consequence

is the change of distortion

Y

Ho = Ce > La > Sm > Nd = Pro by the differing

=

Robinson

Dy > Tm > Lu

The distribution

abundances

is closer Enrichment

to the heavier

Krasnobayev

but will incorporate (1976), Turovsky

(1958).

et al.

(1978) found that Er

=

Gd > Tb

=

Eu ~

of REE in zircon can be REE (Oddo-Harkins

(see Table 3).

The size of

than to the light REE's.

of zircon in the lighter REE's has been reported

Semenov and Barinskii zircons,

=

(Lyakhovich, 1970; Fielding,

1976; Gaudette

of the odd-even

rule) and the ionic radii of these elements Zr4+

and Manukhova,

1975; Medenbach,

In a survey of lZ8 REE analyses,

the REE distribution

explained

1964; Khomyakov

In a study of the REE abundances

by in 6Z

et at. (1976) found that zircon is not selective, what is available.

In addition,

et aZ. (1967), and Khomyakov 75

Krasnobayev

and Manukhova

et al.

(1970) found

1000

:I':

'E

/

that the REE patterns

~~I~j 1/ 0; I

.! .!::! Qj

crystallization.

0 0

c

t::!

.2

m" "'"

" ':;

tI

.S!

i

of other REE-

selective minerals

such as the fer-

the zircons are continually

8000e

0

Better gauges of whether

" I

I

I

I

La

I

I

I

I

I

I

Sm

I

I

crystal-

lizing.

PH20: 2kbar

:: 0.1'

phases which change the

REE pattern of the melt from which

!

gasawa (1970)

1.0

c:

This is attributed

to crystallization

romagnesian

co c.

-...

~~

change during

I

I

Ho

zircon is REE selective

I

I

Lu

tribution

coefficients

or not

are the disbetween

zircons

Figure 4. Experimental par t Lt Jon coefficients for la, Sm, Ho and Lu between synthetic zircon

and the melt from wh i.ch they crystal-

and a felsic, peralkaline (1980) compared with the

lized.

zircon/bulk Nagasawa

silicate combined

.

from Watson range of

rock and zircon/groundmass data of

(1970).

Eu data

is

.

enrichment

(Fig. 4).

by Watson

NaZO-KZO-ZrOZ)

Experimental

and granites

zircon/liquid

at 800°C and P

is similar

(Schnetzler

similarities

REE partitioning

patterns

Uranium,

and Radiogenic

The uranium contents

(1970).

1970), as expected

The concave

some garnet/-

downward pat-

and hornblende/liquid

(Watson, 1980). Elements

of zircons range from 5 ppm in kimberlites

(Kresten et aZ., 1975; Davis, 1976) to 7 wt % U in a pegmatite 1931).

of zir-

The partitioning

and Philpotts,

to zircon.

tern of the heavy REE end resembles

Thorium

coefficients

liquid

= Z kbars are: HZO These confirm the heavy REE enrichment

to garnet

in light of structural

and found heavy REE

(SiOZ-AlZ0 3 La 1.4-Z.l, Sm Z6-40, Ho

cons over silicate melts found by Nagasawa pattern

the

.

partition

(1980) for a felsic, peralkaline

340+, Lu 7Z-lZ6 (Fig. 4).

(1970) calculated .

par t i,t i.on coe f f Lc i.ent s from REE con-

excluded.

tents of zircons and their host dacites

obtained

Nagasawa .

As much as 10 wt % Th has been reported

in zircons

(Muench,

from meta-

somatic rocks

(Pavlenko et al., 1957) and as little as Z ppm in kimber-

litic zircons

(Ahrens et aZ., 1967).

Maximum values of U and Th deter-

mined by microprobe

are 5.06 wt % UOZ and 3.68 wt % ThOZ (Medenbach,1976). High U and Th zircons, which are often metamict and hydrous, are referred to as crytoZites concentrations

and malacons, varietal

names still in common use.

of U and Th in zircon are usually much lower:

The

5-4000 ppm

U and Z-ZOOO ppm Th (Gorz, 1974; Ahrens et aZ., 1967), a fact which is understandable

in terms of the large ionic radii of U and Th (Table 3)76

A wi.de miscibility

gap on the ZrSi0 -USi0 and ZrSi0 -ThSi0 joins 4 4 4 4 In fact, Mumpton and Roy (1961) determined the limits of

is expected. solid solution They believed

in zircon to be 4

±

2 mol

and 4 mol % ThSi0 . 4 4 they synthesized with up to 20 mol %

that the phases which

% USi0

USi04 and 35 mol % ThSi04 were metastable. Caruba et aZ. (1975) ~ere also able to synthesize a (ZrO.8UO.2)Si04 composition but did not comment on its stability.

Zircons grown in a flux with lU0 :2Zr0 were found to 2 2 0.08 mol % U02 by Chase and Osmer (1966). Natural zircons coexisting with U- and Th-silicates and -oxides are

contain

assumed

to have incorporated

maximum

amounts

are among those that have the highest

of U and Th.

U and Th contents

These zircons

but the contents

are still low, indicative of wide miscibility gaps on the ZrSi0 -USi0 4 4 and ZrSi04-ThSi04 joins. Pavlenko et aZ. (1957) found zircons coexisting with uraninite to contain as much as 0.5 wt % U and those coexisting with thorite burg

and thorianite

to contain

up to 10 wt % Th.

(1966) and Silver and Deutsch

thorite

to contain

and thorite

300 ppm U and >100 ppm Th

(Ahrens et aZ., 1967).

Zircons

much lower U and Th contents: 440 ppm in 55 zircons

aZ., 1967; Kresten,

zircons,

1969).

Kresten

and an average

1974; Davis,

ically have U contents and Adams,

in kimberlites an average

have

Zircons

(Ahrens et

in lunar rocks typ-

ppm with a range of 10-1500 ppm (Roger

From data on U contents (1974) deduced

xenoliths

of 5 ppm Th for 6 zircons

1976, 1977).

of 100-400

and mantle

of 47 ppm U and a range of 4.8-

aU.

of rocks and their contained

!U " Z1rcon l 1qu1 d

partition

coefficient

of >100. Ahrens

(1965) and Ahrens

et aZ. (1967) found that the Th/U ratio in

zircons

is less than 1, in contrast

igneous

rocks.

counted

for by either preferential

is closer with

The reason

value of 3.5-4 for

for this is not known, but it could be ac-

to Zr in ionic radius

a Th-enriched

to the general

inclusion

of U in zircon because

it

than Th (Table 3), or cocrystallization

phase such as allanite, 77

monazite

and thorite,

or both.

Pb, Tl, He, Xe and possibly and produced depend

by decay of U and Th.

on initial

ability

Ra and Bi are considered

of zircon

He (Hurley,

The amounts

U and Th contents, to retain

them.

duration

Zircons

of these daughter

of accumulation,

products

and the

may contain up to 0.17 cc/gm

et al., 1956) and small amounts

1952; Hurley

of nonradiogenetic

or common

Increasing

of common lead correlate

amounts

to be radiogenic

lead (Krogh, 1971; Gulson

(0.01-6.5

ppm)

and Krogh,

with increasing

1975).

numbers

of

inclusions. Other

Substituents The remaining

only a singular particularly An added

problem

However,

are necessary

1968).

and Sitnin,

1968),

substitutional Alkali reported

coexisting

reflecting

by Romans

scheme

Nb-Ta minerals

the greater

to metamict

et aZ. (1975), these

(Pavlenko,

elemental

1957; Parker

abundance

=

3

values and

1959; Beus of Nb.

The

2Zr~+.

Na, K, Mg, Ca, Sr, Ba and Ra, have been

earths,

(Gorz, 1974).

CaO is most often reported,

up to 4.6% CaO (microprobe

1976).

of rock.

in zircon.

is (Nb,Ta)5+ + (REE +,Fe +)

ranging

is

70 and 7000 ppm with the highest

3

in zircon analyses

The highest

(4.60 wt %) are for metamict

(Kopchenova

from a large volume

Nb/Ta ratios range from 24 to 110 (Es'kova,

1975, and Medenbach, Na20

of contamination

are often confined

as concluded

are between

and alkaline

concentrations

separated

for charge balance

from rocks containing

are usually minor with often

The problem

is that these elements

zones.

Nb and Ta contents

Fleischer,

in zircons

acute in bulk samples

and hydrated elements

substitutions

high value reported.

values

zircons

analyses

with

by Roman et aZ.,

of CaO (9.00 wt %) and

admixed with other minerals

et aZ., 1974).

The only other elements by microprobe

analysis

reported

in concentrations

are Fe and AI.

than 1.0 wt % by a variety

of techniques

Elements

reported

include

Mn, Ni, Cu, Zn, Ga, As, Mo, Ag, Sn, Sb, Wand

as high as 6 wt % in amounts

less

Be, B, S, Sc, Ti, V, Cr,

Au.

Water Chemical include water,

analyses with

of zircons, particularly

metamict

as much as 16.6 wt % reported

(1961).

Agreement

has not been reached

or water

that has been absorbed

on whether

by metamict 78

zircons,

by Coleman the water

material.

often

and Erd is essential

Frondel

(1953)

Zr(OH)4 Figure 5. Compositions of natural zircons plotted on a molecular basis. Substituents for Zr are not specified. Zircons of the type Zr(Si04)1-x(OH)4X would lie along the ZrS1O,Zr(OH)4 join, whereas zircons with molecular water lie along the ZrS1O,-H20 join. Large circles are literature values compiled by Mumptonand Roy (1961). Small circles are based on microprobe analyses where (OH) is calculated from «Si,P,Al)O')l_x .. (OH)4Xand molecular H20 obtained by difference from the oxide sum (Sommerauer, 1976).

first suggested tution.

that the water

The water

(Frondel,

is often essential

1953; Pigorini

for 137 microprobe

+

P

+

needed

(1962) suggested Zr02·

Mumpton

ZrSi04-Zr(OH)4 Zr02-H20 plot. ZrSi04-H20 largely

and Veniale,

analyses

Al deficiencies

ular water

the amount

in compensating 1966).

of hydroxyl

+

(Si0 ) substi4 silicon deficiencies

Sommerauer

(1976) found that

required

the low totals to 100%.

the solid solution

to balance

solid solutions As evidenced

water,

Dymkov

Si

of molec·

and Nazarenkc

series:

and Roy (1961) pointed

as molecular

(OH)4

in the B-site was much less than the amount

to increase

join, indicating

Infrared,

in zircon represents

ZrSi04-Zr(Si0 )1_x(OH)x-Zr(OH: 4 out that if natural zircons are

they should

in Figure that water

lie along this join in a Si0 2 lie along the

5, zircon analyses of natural

zircons

is present

not hydroxyl.

Raman and nuclear

magnetic

resonance

spectroscopy

show that

both H20 and (OH)- are present in zircon (Dawson et aZ., 1971; Rudnitskaya and Lipova, 1972; Krasnobaev and Ivonina, 1973). In addition, both H 0 2 and (OH)- are in several different sites in the structure, and are aligned 79

either parallel Krasnobaev

hydroxyl

dimensions identical zircon

contents.

zircon

slightly within

+

+

Zr02

H20

smaller

than anhydrous stated.

(1957) synby its IR

Zr(Si04) .75(OH).25 zircon,

It dehydrated

of

although

with

cell

they are

at 750°C, producing

(Caruba et a~., 1975).

From the chemical

cons is minor

and Collette

at 150°C, which was identified

the errors

data, it appears

various

Frondel

Caruba et a~. (1974) synthesized

spectra.

Not surprisingly,

(1973) note that (OH)- is characteristic

zircons with high water thesized

to the e axis.

or perpendicular

and Ivonina

analyses

and experimental

that substitution

and that most water

compositions

and spectroscopic

of (OH)- for Si04 in natural ziris absorbed by metamict material of

as either H20 or (OH) ZONING

Optical

microscopic

etry, fission luminescence Several

examination,

track mapping,

types of zoning growth

growths,

chemical

Chemical

Zoning

passive

zoning,

Distribution electron

(1976), Romans

cause of the sensitivity most effectively

zoning

nescence

(Fielding,

merauer,

1976).

substituting

zoning.

have been studied by

et aZ. (1968), Gulson (1971), Koppel

of the method, by fission

can also be studied

and Wasserberg

(1966),

(1969), Gorz and White

and Sommerauer

(1974),

U distribution track mapping

by

ultraviolet

Be-

in zircons (Fielding,

can

1970;

et al., 1975).

and cathodo-lumi-

1970; Ono, 1974, 1975; Romans et aZ., 1975; Som-

Because

elements,

of the interaction

no simple

color and chemistry

Luminescence)

and out-

et al.. (1975) and Clack et al: (1979).

be studied

Chemical

tensity,

overgrowths

et al., 1974; Grauert et a~., 1974; Fleischer

Yeliseyeva

or cathodo-

on the basis of type or

expitaxial

in works by Steiger

and Grunenfelder

mass spectrom-

are often inhomogeneous.

in zircon crystals

microprobe

Davis et aZ. (1968), Veniale

Sommerauer

zoning,

and sector

of elements

and proton

(1970), Koppel

that zircons

can be distinguished

zoning,

analysis,

color zoning and ultraviolet

have demonstrated

origin:

microprobe

relationship

can be made

• 80

of the large number between

(see PHYSICAL

luminescent PROPERTIES

of in-

These studies have found that the elements which most often subfor Zr and Si, i.e., Hf, Y, P, Ca, AI, Fe, S, Th and U, usually

stitute increase

together.

The zoning is best described

there is a general

trend of enrichment

and Si toward the rim. nearly

physical

are represented continuous

by intergrowths

two immiscible,

and compositionally

temperature

to radiation

damage, water-rich,

of

in HF, more

unstable with increasing

Strongly

zoned zircons produce

data are explained by a mixing

and almost concordant

dant system consists

intergrowths

impure zircon differ in physical

and diffuse Pb more easily.

discordant

zoning

et al., 1968).

They are more soluble

ages, and chronological

and

their coexis-

as epitaxial

(cf. Grunenfelder

phases

zones of

Because of the lack of

zircon and xenotime,

from the purer zircon.

susceptible

highly

of xenotime.

for Zr

composition

cases of compositional

can be interpreted

isostructural

Both xenotime properties

discordant

Extreme

solid solution between

tence in zoned crystals

produce

with zircon of variable

properties.

although

substituting

These chemical substitutions

ideal zircon intergrown

different

as oscillatory,

of elements

systems.

of the compositionally

of

The highly discor-

impure zircon zones, which

were called "hot spots" by Steiger and Wasserberg

(1966) because of

their elevated U and Th contents.

system is the nearly

ideal zircon. systems.

Sommerauer

It remains

The concordant

(1976) described

to be seen whether

simply a result of strong compositional taxial intergrowths

of immiscible

them as two-phase

this phenomenon

zircon

in zircon is

zoning, or the result of epi-

~hases or of exsolution.

Growth Zoning Much of the chemical

zoning in zircon results from growth in a

silicate melt, as evidenced sult from physical from which tion.

and chemical variations

the zircon crystallizes

The chemical

zircons,

variation

1963; Gottfried

et al., 1968).

advanced by Rosenbusch early.

zones re-

in the melt or solutions reequilibra-

textures of

with grain size are cited

crystallizes and Waring,

This is in contrast

in a cooling magma 1964; Kohler,

The zircon cores reflect

1970;

to the more classical

(1882) that small, euhedral

of the melt and the zoning reflects

Growth

and lack of subsequent

that zircon continually

(Silver and Deutsch,

crystallize

habit.

zoning, seriate and hiatal

and bulk compositional

as evidence

Veniale

by its euhedral

accessory

minerals

the initial composition

the changes as crystallization 81

ideas

pro-

CONTINUOUS

GROWTH

HISTORY

o o

ceeds, eventually

expected

zoned

unzoned

DISCONTINUOUS

GROWTH ~

oyergrowths

zircon

(of

in the late-stage

In Sri Lanka

or xenotime)

described

by differences

partial aggregate crystals also called synn .... is or parallel growlh

lotal

(B

zircon

from rhythmic

fringence

bands:

is defined colors

by strain

rate.

in

Some fine bands

and densities.

bire-

(2) These

high density bands are the most crystal-

hemispherical

present.

(3)

banding is superimposed

Figure 6. Df.a g r-amma tic representation of the terminology applied to zoning in z Lr co ns . The shaded sections are the earlier generation zircons.

by greater

in birefringence

(B

diation

=

Coarse

on the fine and

is characterized

correlated

differences

0.010 - 0.050)

with varying

degrees

of ra-

damage.

Zoning

Zircons of elements

in which without

Outgrowths

chemical

new growth

(1974), for example, rims without

zoning

found that zircons

new crystal

zoning.

in a quartzite

or addition Grauert

et aZ.

gained U on their

growth.

and Overgrowths

Zircons

in metamorphic

or xenotime.

and igneous

Figure 6 presents

these zircons.

The different

tically, but also can differ metamorphic original

is caused by removal

is termed passive

cores which have been epitaxially

rocks,

igneous

well-rounded crysts

(1981)

fluctuations

relief and higher

line portions

Passive

(~3 µm wide)

(~lO) and may be caused

have strong

pyramidal

melts. Sahama

in interference

crystallization

or xenotime)

zircons

0.001 - 0.002) and extinction

resulting

COriS

(of

=

angle

anhedral or detrital

outgrowths

a rim rich

three types of growth

(1) fine banding

.uhadrol cores

@

producing

in Hf, U, Th, Y, REE and P, as might be

rocks often contain distinct

overgrown

by later generation

the terminology generations

that has been applied

can often be distinguished

in chemical

and isotopic

composition.

the older zircon cores have been inherited

or sedimentary

detrital

grains.

from either the adjacent

zircon

country 82

In

from the

rock, so they are either euhedral In igneous

to op-

or

rocks the older cores are xeno-

rock or the source area.

It is

this persistence, its reputation

evidenced

by these older cores,

as a stable

and refractory

There have been numerous con on prexisting,

rounded

reported

detrital

of zircon under high grade contact 1950; Taubeneck, Grunenfelder, felder, Gulson

and Krogh,

metamorphic growths

have received

attention

case, the upper

ferences

in isotopic

end-member

ZrSi04

and removal resistance ering,

to be the combined

ZrSi04

and isotopic

metamorphic

With increasing

changes

grade were

metamorphism

change

Overgrowths ported

in identifying crysts

is readily

and mechanical

weathand re-

by Davis et aZ. (1968).

aureole,

recognized,

the age of the magmatic

yielding

derived

by partial

granites

melting

of zircon

rocks have been re-

problems

in age dating

source region.

Zircon xeno-

(c. 400 Ma) have U-Pb

Ma and are believed

of Proterozoic

and Pidgeon,

83

crust at depth

1976; Pidgeon

in sedimentary

(1970).

age can be of great interest

of Scotland

dates of 1000-2000

1974; Pankhurst

they found there on the rims, with a

et aZ. (1968), and Kohler

the discordant

in the Caledonian

The persistence

abrasion

the greater

during annealing

in igneous

(1950), Veniale

However,

systems

Johnson,

con-

age (Fig. 7).

on zircon xenocrysts

this new growth

can be avoided.

These authors

that occur in zircons with in-

demonstrated

in a contact

in apparent

by Poldervaart

Because

(1971) and

of mechanical

was loss of Pb and gain in U and Th, particularly resulting

to dif-

of zircon.

The chemical creasing

rims.

to chemical elements

In

cores to be nearly

zones rich in other elements,

of near end-member

ages.

In addition

detrital

result

as a

with over-

is the age of the older

and Grunenfelder

to the overgrown

1974;

is described

Zircons

of their discordant

Koppel

and the loss of substituting

crystallization

zircon

intercept

and Grunen-

and Sommerauer,

1925).

(1974) found the older,

of outer growth

(Poldervaart,

et aZ., 1967; Koppel and

the age of overgrowth.

as compared

sider this phenomenon

because

composition,

and Sommerauer

in which

(Gillson,

concordia

cores and the lower intercept

Koppel

metamorphism

1969; Koppel

Occurrences

are uncommon

of zir-

or of the recrystallization

1963; Gastil

and Yamaguchi,

1975).

mineral

the simplest

zircons

of the overgrowth

1967; Davis et aZ., 1968; Tilton

1967; Ishizaka,

1968; Ishizaka

zircon gets

mineral.

examples

or regional

1975; Schidlowski,

from which

to have been (Pidgeon and

and Aftalion,

and metamorphic

processes

1978). is

et al., (1979) to

used by Halliday suggest

the Caledonian

granites

could have also have come from

~

~ sediments

,;

~ terozoic

derived

from the Pro-

crust.

c

0 u

-;;. E

~ Sector Zoning

~

I

>(110)

ACIDE

NEUTRE

zr~1

850'

(I)1(110)

~

COMPOSITION

(IOO)uuc

---...._____

(IJi(110)

BASIQUE

TVPES

J.P.PUPIII.o.TUIICO.,,111

9-· ai,

DE

CU551FlCATIOH

o

I'II'IMI

~®.o. ©.~ q, $@~ .....

Aa.

Figure 8c. Changes in zircon morphology with estimated temperatures of crystallization of the host rock (see Pupin and Turco, 1972; 1975).

based on both experimental

and petro-

logic studies: (1)

Crystallization

rate:

long, prismatic

crystals

Poldervaart, (2)

Acidity:

rapid crystallization (see Fig. 8; Kostov,

is found to favor 1973; Larsen and

1958).

increasing

acidity

favors more tabular crystals

Fig. 8b; Caruba et al., 1975). 85

A

(see

(3)

Agpaicity:

related

cons in agpaitic 1978; Kostov, Marchenko (4)

Temperature:

alkaline

the development

content

drous magmas

rocks

of bipyramidal

(K

+

zir-

Na > AI) (Caruba,

1975; Poldervaart,

1956;

1966; see Fig. 8a).

decreases

Pupin and Turco, Water

or hig~ly

1973; Pupin and Turco,

and Gurvov,

{lID} prims

(5)

to (2) is the occurrence

of the {100} prism increases

with increasing

temperature

and

(see Fig. 8c;

1972, 1975).

of the melt: whereas

{lID} prisms

{100} prisms

dominate

are dominant

zircons

in hy-

in dry magmas

(Pupin et al., 1978). (6)

Variation

in zircon chemistry,

substitution

H20 are presumed to favor bipyramids habit (Kostov, 1973; see Fig. 8a). (7)

Crystal

size:

developing Jocelyn

zircons

of decreasing

temperature

Zircon

overgrowths

thonous

granites

(9)

Zircons

from kimberlites

another tion.

(Poldervaart

of the magma

and Turco

1972;

This may be the result

rocks are characteristic and Eckelman,

to relate

1955).

(Kresten et aZ., 1975).

are rounded

are not independent

the morphology

(1975) conclude

of autoch-

of one

to anyone

that temperature

condi-

and agpaicity

are the most important.

Using morphology quantifying

1970).

zircon morphology

and it is difficult Pupin

{lID}

(Fig. 8c).

in igneous

affecting

Hf favors prismatic

face over {100} (Pupin and Turco,

1974; Kohler!

(8)

These conditions

whereas

change in crystal habit with growth,

as the dominant

and Pidgeon,

of U, Th, REE, P and

as a petrogenetic

observations

indicator

on a large number

requires

of crystals.

a method

of

Several methods

have been used: (1)

Statistical by graphical

studies

of crystal

comparisons

length

(x), width

method

of the reduced major

where

the length

are measured

dimensions.

of frequency

(y) or elongation

and width

axis

this was done

(x/y).

This evolved

(Alper and Poldervaart,

of a number

and the following

Initially

curves or histograms

of unbroken

of into the 1957)

crystals

(~200)

calculated:

x, mean length;

Sx' standard

y, mean width;

S , standard

In a plot of length versus width,

y

the point

deviation

of x

deviation

of y

(x,y) is

plotted

and

y

p

p

o

PRISME

B

$,

R

!~ 0,

{110} > [100 I

s {lOa} ; (11O)

$

~

~

A

R

AB1

@LI

e e

@"

@

~

~

{WO} >{110 I E

{lOOl» {110 I

s

A

0 g 0 0 0

L3

~

LS

s

'3

'2

L,

Gl

'5

G3

100

~

@'6

~

~

'7

'8

'14

@OS

~, 100

"8

©'22

'23

e)

.~ ... ./

'17

®,

200

Jl

.

200

N Types and subtypes 1972)

J2

300

0 g

D

P,

400

fundamental

500

c

D

P2

©"

P,

'25

Ps

0

JS 600

C

500

0

700

of

zircons.

T 700

'5

®,

800

800

(After

Pupin

..-'

•

"110

Figure 10. (a) Stereograph1c projection of zircon (after Caruba and Turco, 1971); (b) poles to principal, cleavage planes (large filled circles) and subordinate fractures (small, open circles) in kimberlite zircons (after Kresten et al , 1975). 1

87

E

600

A

E

to the classification

400

©'2

'3

'20

Q

J4

J3

N

300

P3

'24

I

C

© '9 © '10 @@, @@ ©@ ~@ @@ *$ @,@ @@ '13 '15 '" @o, @ '16 © © © "9 © g ~" 0 g 9 0 G @'21 ~02

{roo}

Figure 9. and Turco,

$~

ABS

O~2

03

M

s

E

$

AB,

AB3

"2

©L2

o

M

a line, the slope of which is S Is , is drawn through the point. y x The end points of the line are obtained by omitting 2.5% each of the largest

and shortest

tions can be compared

(2)

either visually

major axis of a group of zircons

is supposed

to approach

Fourier

is resolved

The sum of the harmonics

shape.

amplitudes

The harmonic

amplitudes

which

Predominance

are compared

system of Pupin and Turco porates

1978).

indicate

suggested

development

studies

the grain contribu-

to another.

crystal

forms.

setting, which

The

and incor-

back to 1886.

of pyramid

It is

and prism faces which

in Figure 9 (from Pupin et aZ.,

are made on unbroken

by Caruba and Turco

gram for identifying

describe

(1972) is the most extensive

which are grouped by similarity morphological

of shape compo-

from one population

on a grid reproduced

Statistical

The two-dimensional

the relative

prism and pyramidal

the ideas of the earlier workers

are summarized

rock

to the total grain shape, and it is these

of principal

based on the relative

in an igneous

into a number

nents or harmonics.

tion of each harmonic

tests.

the growth trend of the zircon crystals. (Byerly et aZ., 1975).

shape analysis of zircons

Zircon popula-

or by statistical

The reduced

projection

(3)

crystals measured.

to the habits

zircon crystals

of the grid.

is also the x-ray setting, (1971), who also presented

and classifying

The

is that a nono-

the faces.

Twinning The commonly geniculate

reported

growth twins.

twin plane in zircon is {101}, which produces This plane coincides

with layers of isolated

Si0

tetrahedra. A mirror plane would produce a twin-member whose struc4 ture would have a 1800 rotation about [101] from a continuation of the untwinned twinning

crystal.

Recent work and summary of previous

is given by Jocelyn

and Pidgeon

work on zircon

(1974).

Cleavage The most commonly matic and parallel

reported

cleavage

in zircon is imperfect,

to {lID}, a plane which

is parallel

pris-

to the edge-

sharing

Si0 -Zr0 chain and is also parallel to what is the nearest ap4 8 proximation to a close-packed layer of oxygen atoms in zircon. Kresten

et aZ. (1975) found that in kimberlitic

zircons

{DOl} and {lll} are the

most frequently {113} observed

developed

cleavages

with

(Fig. lOb) in addition

{110}, {2l0},

to a number

tures and partings.

Many of these cleavages

as would be expected

because

ings.

Pronounced

a plane of weak Rather

parting, adhesion

such as between

than exsolution,

positionally

the weak adhesion

different

growth

{33l} and

are not equally

of the symmetry,

traditionally

{3l0},

of subordinate

suggesting

attributed exsolved

frac-

developed

they are part-

to twinning, phases

may be

(White, 1979).

in zircon may be between

zones which may differ

com-

in metamictization

as well. Optical

Properties

Zircon indices

of

interval mond,

is uniaxial E

=

1.984 and

of visible

accounting

substitute persion

positive,

w

1.924.

light, which

the widespread

of the refractive and Krylova

=

zircon has refractive

Dispersion

is close to 0.04 for the

is just slightly

for the fire of cut zircons

before

Il'inskiy

=

and synthetic

and its use as a diamond

availability

indices

of synthetic

to n at A

fractive

index of 1.98, zircon has a reflectivity

activity

in density

relationship

(see Density

1964; Ueda,

gives

with meta-

1935) or radio1955).

using a density and constants

value

from

of 3.96 for metamict from Mandarino 0

with a 2V up to 10

are biaxial

The

1.81 as a limiting

the value of 1.83 calculated

section below)

specimens

decrease

(Chudoba,

and Gottfried,

zircon approachs

This agrees well with

Some metamict

With a mean re-

of 11% which

and birefringence

by changes

index of metamict

the Gladstone-Dale zircon

indices

as measured

(Fig. 11).

by

luster.

(Morgan and Auer, 1941; Holland

refractive

Dis-

for the dispersion

589.3 mµ are given in Table 4.

Both the refractive mictization

gems.

of zircon have been measured

(1974) and their corrections

relative

it ~ subadamantine

less than that of dia-

(1976).

(Krstanovic,

1956), but most are isotropic.

Hafnian

E

=

zircons with 21-31 wt % Hf02 have refractive indices of 1.97 and w = 1.92 (von Knorring and Hornung, 1961). The slightly

lower refractive

indices

of hafnon

stone-Dale

relationship

for zircon

and 1.946 for hafnon,

the sYTlthetic material

would be predicted

which yields

mean refractive

using the densities

of Salt et al.

89

from the Gladindices

of 1.980

in Table la for

(1967) and constants

from

Table 4. ).,

Meancorrections c

mµ

435.8 486.1 500.0 546.1 578.0

for the dispersion

.

£-w

w

of zircon (II' Inskiy and Krylova, 1974) e

A. mlJ

£-w

---

---

---

--

---

---

-Hl.0287 -Hl.0166 -Hl.0138 -Hl.0058 -Hl.OOB

-Hl.0271 -Hl.0155 -Hl.0130 -Hl.0055 -Hl.0012

-Hl.0016 -Hl.0011 -Hl.0008 -Hl.0003 -Hl.0001

589.3 620.0 656.3 700.0

--

0.0000 -0.0033 -0.0068 -0.0101

0.0000 -0.0032 -0.0066 -0.0097

0.0000 -0.0001 -0.0003 -0.0004

(1976). Variation

Mandarino

often largely obscured

of optical properties

W

with composition

by the effect of metamictization

is

in zircon.

Color Zircon is found in colorless, brown and grey hues. although

Colorless

color can be sometimes

transparent spectrum,

green, blue, red, orange, yellow,

stones are often obtained

by heating,

restored

Colors of

by y-radiation.

solids are a result of absorption

(up to 36 bands) which identifying ficiently

are sometimes

cut gemstones. to determine

outlined

by Nassau

presence

of uranium

distinctive

enough

its origins

(1978). Color centers may be associated and can be sector zoned, concentrated

of Nb+4 ions produced I

!'un

with the or most in-

1970).

(Fielding, 'n

nw

A &'" 0 C 1'37 .,••' _ .0 0

C.

'.00

.'"• ,e'

"I

L I

o

o,A

~c. ... ~

6 021-/ '"

6.8

.. Metamict

t:>yc.",

0< .

.

I

I

I

"...,

606[

"

,>-;

6.70 I ~ ., I" •••

I

, ~o~

5.981-

0

43 / ~ ~.0 0

66

780 065

I- hafnon...

...

5.96 6.56

;".' 53

t:>"

~

6.58

47

'"q' zircon ••

0 6.60

0

OH zircon

O,A

6.62

0 6.S-4

Figure 13. (a) The cell parameter a as a function of " for silicates and phosphates with zircon-type structures. Lattice parameters for zircon and hafnon from Table 1. References for the lattice parameters of the actinide orthosilicates are given in Chapter 10; the REE orthophosphates are from Muller and Roy (l974). Metamict zircon is from Figure 13b. (b) a as a function of c for Ceylon zircon showing trend of increasing a activity which varies from 0 to 1000 a/mg/hr (data from Holland and Gottfried, 1955). (c) a as a function of " for synthetic zircon and hafnon and structurally analyzed zircons from Table 1. Additional data from Subbarao and Gokhale (1968), Ozkan and Ja.ieson (1978) and Caruba et aZ. (1974). Synthetic OH-zircons from Frondel and Collette (1957) and Caruba et aZ. (1974). Hafnon-zircon solid solutions from Correia Neves et at. (1974); the numbers are Hf/(Hf+Zr).

92

7.2

6.61 6.60

~ .... 2?

6.59 6.58

Q)

E

6.57

o 0..

6.56

~ Q)

£e

5.98

..J

5.97 5.96

0

20

40

60

80

100

Mole % HfSi04 Figure 14. Variation of lattice parameters with composition in the system ZrSi04-HfSi04' (After Ramakrishnan et aZ., 1969.) 6·10,10

V

I>

IU

-- -

01 1/ f

6·05 0

1

f .f ~

c 6·00 o

1/

r

(Q)

!

5·97'0

I

!V p-tr

6-700 )

a

j

;, Y'

6 6·600

-

!

V ,

.f.--

, (b)

r

) 6·650

r> o

Ii 7'

-

In

I I (~/mg/hr) 800 'I 1200 0·449 0·693 Dosage (10'6a/mg.) Activity

400 0·224

_ I--161o 0·898

Figure 15. (a) The cell parameter e (in Angstroms) and (b) a (in Angstroms) for Ceylon zircon as a function of the present ~ activity and total a dosage, i.e., metam1ctization. (After Holland and Gottfried, 1955.)

93

(1955) found that the a and c cell dimensions

Gottfried

with a activity

and level off above 800 a/mg/hr

6.090 A (Fig. 15).

The expansion

of cell parameters

coincides

with a line drawn between

silicates

(Fig. l3a).

cons used by Holland

Subsequent

less than would be required that enlargement by radiation.

=

increase

with a activity ortho-

of the composition

of zir-

(1955) show no more than 0.006 wt % U

to expand

and Fairbain

This amount is much

the cell dimensions,

results

indicating

from structural

(1953) suggested

damage

caused

the degree of zircon

from the d

can be estimated

28

rapidly

6.708 A and e

zircon and the actinide

et aZ., 1956).

of the cell volume Hurley

metamictization approaching

normal

determination

and Gottfried

(Pidgeon et al., 1966; Gottfried

=

at a

35.1° from a value of 28

=

-spacing, asymptomatically l12 35.635° for nonmetamict zir-

con. l3c is an a versus

Figure

talographically of the synthetic

a

=

=

5.979.

zircon metamictization

Collette

This suggests Hardness

Most

fall in a cluster near determinations

synthesized

by

of these strucby Frondel

and

et aZ. (1974) have smaller e dimensions than zircon.

The hydroxyl

trend, suggesting

However,

the variation

but above it displaced

(OH)4 ~ Si.

solid solutions

(1974) have increasingly

along

but

zircons

do

that water-bearing

the substitution

the zircon-hafnon

with Hf substitution. non and zircon,

zircons

the differences

zircons

zircons have not undergone

Neves et aZ.

Correia

Hydroxyl

the metamictization

be predicted,

and crys-

(1958) (Table la) fall along the trend of

or larger a dimensions

not fallon

or chemically

from the literature.

used in structural

and may explain

(1957) and Caruba

comparable

metamict

analyzed

Zircons

(1974) and Krstanovic

tures from the others.

would

zircons-hafnons

and structurally

6.604 A and c

Finger

c plot of synthetic

characterized

described

smaller

lattice

As by

parameters

does not lie between the metamictization

haf-

curve.

that they are metamict.

and Elastic

Properties

Zircon has a hardness to 1468 kg/mm2.

of 7~ and a micro-indentation

The hardness

of 485 to 841 kg/mm2•

of metamict

Nonmetamict

zircons

hardness

of 841

is less, with a range

zircons have a hardness

anisotropy

of

1.22. Elastic atures

properties

of 25-300°C

have been measured

over a range of both temper-

(Ozkan et aZ., 1975) and pressures 94

of 1 atm to 48 kbar

(Ozkan and Jamieson, are reported

but several

compressibility coordinated temperature

conclusions

coefficients

Si.

pressures.

derivatives

refinements

Zircon has the lowest

substance

unstable

of zircon's structural

transformation

The elastic mict zircon

(a

elastic

(see STRUCTURE obtained

6.606(2) A,

and the

constants

transformation

are

at higher

from the high pres-

(1979), a zircon

KAlF 4 Si is predicted

with octahedrally-coordinated

constants

=

with tetrahedrally

with pressure

of Hazen and Finger

to occur at about 160 kbar

= =

A range of values

Based on the Si-O bond compressibilities

sure structure

cll

becomes

with a zircon-scheelite

1979).

can be drawn.

of any measured

The structure

and pressure

consistent

structure

1978; Hazen and Finger,

+

section).

from synthetic

zircons and nonmeta-

5.980 (2) A) by Ozkan et al.. (1974) are

Cl

4.237, c33 = 4.900, c14 = 1.136, c66 = 0.485, c = 0.703, and 12 12 2 1.495 (all times 10 dyn/cm ). A systematic and marked decrease

c13 of up to 69% in the elastic module metamictization tic moduli approach

(Ozkan, 1976).

decrease

of zircon is noted with increasing

All the longitudinal

with radiation

two common saturation

The decrease

interatomic

and lattice

bonding

damage as measured of 1.5 x 1012

values

cm2, respectively.

and the shear elas-

in elastic moduli spacings

by the density

and 0.49 x 1012

and dyn/

result from changes

caused by disruption

in

of the

structure. In relating Kieffer

lattice-vibrational

(1979a,b,c;

heat capacity

and calorimetric

Her model uses published data for a number Thermal

to thermodynamic

1980) calculated

the temperature

Debye

elastic,

of minerals,

temperature

between

crystallographic

inclu~ing

of the

0 and 1000oK.

and spectroscopic

zircon.

Properties

The most recent and Gokhale

determinations

(1968) and Worlton

of thermal expansion

et aZ. (1972):

a Cl

thermal

properties, dependence

expansion

coefficient

25 and l300°C, making is this property

a

of zircon is small, 4-5 x 10-6/oC between

it relatively

which makes

are by Subbarao

> a , and the bulk

insensitive

to thermal shock.

zircon ideal for use as foundary

It

sands and

refractories. The thermal ford, 1965). the thermal of phonons

conductivity

Exposure conductivity

of zircon is 120

to a radiation

±

10 cal/oC cm sec (Craw-

dosage of 30 x 1019 a/cm2

to 23 cal/oC cm sec because

by the radiation-induced

defects.

95

decreases

of the scattering

Luminescence Luminescence sponse

is the emission

to ultraviolet

.. ..

light

of visible

light by a material

(photoluminescence

in re-

or fluorescence),

energetic

100,.·..,

CD

c

~o

o Q. CD-

a:~

G';;

l:!; u C "'.-

10

CD_ CD C

CD

...I

CD

>

'e::: ::0,2

0-

lD-

."

o

o.s

:: c u

0.10

2

I

4

Trace

6

8

10

wt. "10 oxide

and minor elements,

Figure 16. Variation in cathodoluminescent intensity with the amount of trace and minor element substitution in zircon (Sommerauer,1976).

electrons

(cathodoluminescence)

chemistry

and structure

or heat

affect

(thermoluminescence).

the 1uminescene

properties

Activators

in zircon are one or more rare earth elements

(Fielding,

1970; Caruba et aZ., 1974; Trofimov,

the effects

of REE's,

lead to quenching

of the luminescence

cathodoluminescence

intensity

(Sornmerauer, 1976). (1) in studying tive manner

as well as increasing

compositional

therrno1uminescent

properties

section.

Materials

potential

phosphors.

of the contained a subject

scientists

A rapid drop in

or semi-quantita-

(2) in correlating zircons,

discussed

have investigated

and (3) in

in the GEOCHRONOLOGY REE-doped

zircons

METAMICTIZATION Metamictization effect of radiation

in minerals

is generally

damage produced

considered

by radioactive 96

of

can

of zircon have been used

zoning in a qualitative

age dating,

Interaction

at about 2 mol % REE

(Sornmerauer, 1976; Ono, 1975, 1974),

rock types based on similarity

of a material. or uranium

REE concentrations,

(see Fig. 16).

was observed

The luminescent

1962).

Both

to be the

decay of thorium

as

and uranium.

General

reviews

Billington

and Crawford

Chadderton

(1965).

Pellas

Earlier

(1954) and Holland

consists

of displaced

of metamictization

(1961), Crawford summaries

and Gottfried

(1955).

atoms, vacancies

structure

in

and the ionization

the course of radioactive The intensity

into an optically

Bursill and McLaren, calculated

necessary

structure

1966).

damage in crysta

atoms

(including

the atoms in the un-

and high temperatures

generated

decay.

of radiation amorphous

between

are given by

y rays, and heavy charged particles

and a particles,

and from nuclear recoil,

Radiation

and interstitial

(1952),

(1973), and

of zircon metamictization

helium) which result from elastic collisions disturbed

are given by Pabst

(1965), Mitchell

Pellas

is

to convert crystalline 1015_1016

a/mg

(1954) and Holland

that zircon appears amorphous

zircon

(Woodhead,

1978;

and Gottfried

(1955)

to x-rays when 20-30% of the atoms

are displaced. Bursill and McLaren's showed that no radiation a/mg and that metamict crystallites

(1966) transmission

electron microscopic

to 7.

and E. W. White (1970) Minor and trace elements --Petrol, 29, 180-182.

in HF-soluble

(1956) Age determination

of igneous

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Contrib.

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improved

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Syme, R. W. G., D. J. Lockwood and H. J. Kerr (1977) Raman spectrum of synthetic and thorite (ThSi04)' J. Phys. C: Solid State Phys., 10, 1335-1348.

zircon

(ZrSi04)

Taubeneck, W. H. (1957) Zircons in the metamorphic aureole of the Bald Mountain batholith, horn Mountains, north-eastern Oregon. Bull. Geol. Soc. Am., 68, 1803-1804. Tomita, T. and Y. Karakida (1954) Effects of heat on the color and structure Mamutu, Formosa. Japan. J. Geol. Geogr., 25, 145. Trofimov,

A. K. (1962) The luminescence

spectrum

of zircon.

Geochem.,

of hyacinth

of zircon.

Mem.

from

II, 1102-1108.

Tugarinov, A. I., E. E. Vainshtein and I. D. Sheva1leeskii (1956) Hafnium-zirconium zircons of igneous and metasomatic rocks. Geochem., 4, 361-374. Veda, T. (1956) On the biaxialization 297.

Elk-

ratio in the

ColI. Sci. Univ. Kyoto B. XXIII,

No.2,

Vainshtein, E. E., A. I. Tugarinov, A. M. Tuzova and I. D. Shevaleefskii (1958) Hafnium-zirconium ratios in metamorphic and metasomatic rocks. Geochem., 3, 305-309. , A. I. Ginzburg and I. D. Shevaleefskii ------pegmatites. Geochem., 2, 151-156. Vance,

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______ and B. W. Anderson

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analysis,

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Effects, zircons.

24, 1-6. Mineral.

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Part II, the zircon

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V1asov,

K. A., editor

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112

Chapter 4

J.

The ACTINIDE ORTHOSILICATES INTRODUCTION: The lighter,

Each of these silicates

zircon and hafnon. isostructural

OCCURRENCES

actinide

formula AB04' where B

with the general or Am.

tetravalent

A. Speer

elements

=

form orthosilicates

=

Si and A

is tetragonal

Th, Pa, U, Np, Pu

and isostructural

Th and Pa also form monoclinic

polymorphs

with that are

with monazite,

CeP0 (see Fig. 1). Three of the ac4 are found in nature: tetragonal ThSi0 , tho4 rite; tetragonal USi0 , coffinite; and monoclinic ThSi0 , huttonite. 4 4 A summary of earlier work and historical information concerning these tinide orthosilicates

minerals

is given by Frondel

and discusses Although are widespread

related,

Because

but incompletely

relatively

minerals

ore minerals

they are commonly

of the actinide mineralization.

He also includes described

rare in nature,

accessory

and are important

(1958).

orthosilicates The minerals

the actinide

in origin,

T

P

y. -

t ~I

a.

-

I· p. h Pu I uttonite A· .mtf

Q)

E

:

/

=U

coffinite

280

N

./

material

Po

spectra

the

of the

states of

rare earth and actinide elements which are used in phosphors.

They con-

crystalline

hosts

which are optically -

transparent, in fluxes,

U Q)

studies

for studying

higher valence

stitute

Th /

rocks

and thorium deposits.

geochronologic

electronic

3201-

orthosilicates

have been used to obtain ages of also provide

thorite =Th

names

substances.

in igneous and metamorphic

in some uranium

primary

varietal

easily grown readily

doped

with lanthanides uranium, 2601-

--

•• Zr = zircon /

Hf = hafnon

vide sites of tetragonal symmetry

0.8

0.9

1.0

Ionic radius,

A

1.1

and

and which pro-

cations

for tetravalent (Table 1).

Most of the natur-

Figure 1. A plot of the unit cell volumes of the actinide orthosilicates versus the effective ionic radius of the tetravalent actinide in 8-fold coordination. Radii from Shannon (1976) .

113

ally occurring

thorites

that have been described

are from pegmatites

associated

nepheline

or from placer concentrations

syenites,

Less commonly, posits

thorites have been described

(Phair and Shimamoto,

use of the electron spread accessory normal

thorium

1970; Renard,

from them. de-

The increasing

that thorite is a wide-

of igneous and metamorphic

rocks which have

(Silver and Deutsch,

1963; Willgallis,

A lunar occurrence

is re-

et aZ. (1972). occurs as a primary ore mineral

uranium-vanadium

It is associated

(Abdel-Gawad

is found in hydrothermal, minerals

of uranium

ores of the Colorado

with or replaces

woody origin or asphaltite

Co-Ni-Bi-As

or

derived

from hydrothermal

has revealed

1974; Speer et a~, 1980).

Coffinite unoxidized,

microprobe

mineral

syenites

1952) and from skarns.

concentrations

ported by Haines

posits.

with granites,

Plateau-type

carbonaceous

de-

material

and Kerr, 1961).

vein U deposits

or Mo (Ramdohr,

in the

of

Coffinite

with pitchblende, et aZ., 1963).

1961; Darnley

Table lao Crystallographic data for actinide orthosilicates with the zircon structure (space group I4 /amd).

1

Atom

Site

A Silicon Oxygen

4a 4b 16h

End-

Point

symmetry

o o

o

Cell dimensions

a

member

Coordinates

42m 42m m

Coordination

3/4 3/4

1/8 5/8

x

z

density gm. cm-3

8 4 3

Calc.

"

Reference

7.1328(2)

6.3188(2)

6.70

Taylor & Ewing (1978)

7.068(7)

6.288(6)

6.832

Keller

(1963)

6.994 (5)

6.263(5)

7.164

Keller

(1963)

NpSi04

6.950(7)

6.243(6)

7.254

Keller

(1963)

PuSi04

6.906(6)

6.221(6)

7.415

Keller

(1963)

AmSi04

6.87(1)

6.20(2)

7.561

Keller

(1963)

ThSi04 PaSi04 USi04

Table lb.

Crystallographic data for actinide-orthosilicates monazite structure (space group P2 /n) . 1 Site

Atom

A Silicon Oxygen (1) Oxygen (2,3,4)

Point

4e 4e 4e 4c

symmetry

1 1 1 1

Coordinates x :;;

a:

x

Cell dimensions

y Y y y

z z z z

Calc. density gm cm-3

with the

Coordination 9(8) 4 4

a

b

"

ThSi04

6.784(2)

6.974(3)

6.500(3)

104.92 (3)'

7.25

Taylor & Ewing (1978)

PaSi04

6.76(4)

6.92(4)

6.45(5)

104.83(25)'

7.36

Keller

6.920

6.434

103.83·

5.47

Rao & Finney (1965)

cheralite 6.717 (Ca,Ce, Th) (P,Si)04

114

Reference

(1963)

As in the case of thorite, increasing use of microtechniques has shown that coffinite also occurs as a disseminated accessory mineral of igneous and metamorphic rocks (Zavarzin, 1977; Speer et aZ., 1980). Huttonite is commonly encountered as an ignition product of metamict thorite and is rarely reported as a naturally occurring phase.

Most published accounts list huttonite as a constituent of

beach sands, presumed to have been derived from metamorphic rocks. Huttonite has also been found in a hydrothermal vein associated with a granite in a metamorphic terrain (Kosterin and Zuev, 1962) and an unspecified occurrence in metamorphic rocks at Sudbury, Ontario (Traill, 1969).

CRYSTAL STRUCTURE Thorite Thorite has long been accepted to be isostructural with zircon on the basis of the crystal habit and chemical composition.

This

was first conclusively established by Pabst (195la) in an x-ray study.

Thorite and the zircon group possess a body-centered, tetra-

gonal unit cell with space group symmetry I4 /amd. The general l chemical formula is AB0 with Z=4. The A and B cations occupy 4

special positions fixed by the space group symmetry, but the y and positional parameters of the oxygen are variable (Table la).

z

The 0

positional parameters have twice been obtained on synthetic material by powder methods:

Fuchs and Gebert (1958):

a = 7.l42A, c = 6.327A,

Y = 0.084(10), z = 0.222(10); and Sinha and Prasad (1973): a = 7.l48A, c = 6.309A, Y = 0.081, Z = 0.232. The most recent refinement was on a flux-grown single crystal by Taylor and Ewing (1978): 7.l332A, c = 6.3l9A,

Y = 0.0732(13),

Z

= 0.2104(16).

a =

The following

description of the structure is based on their work. In thorite, Th is surrounded by eight oxygen atoms in triangular dodecahedral array, with four "equatorial" oxygens at distances 2.37A and another four "axial" oxygens at 2.47A which are denoted by primes in Figure 2b.

Each pair of adjacent "axial" oxygens is bonded 115

0("

?

OOl? oor

O'" -===D,.-i 012"

~

o

O,,~(

~

-=..:..:. (y--

< ,

00121

0)4"

h

~,_j

(> (a)

,

0-< b

,_j (b)

Figure 1. The a-axis chains in (aJ huttonit. and (bJ thorite. After Taylor & Ewing (1971 (a)

L.

Figure 2. Th environments in (aJ huttonite and (bJ thorite. Open circles are 0, gray circles are 5i, and black ellipsoids are Th. Axial and equatorial atoms have primed and unprimed labels respectively. After Taylor & Ewing (1978).

°

(a)

Figure 4. Perspective polyhedral representation of the (aJ huttonite, and (bJ thorite structures. Darker tetrahedra are 5i0 groups and lighter polyhedra are (aJ Th04 and (bJ Th08 groups. After Taylor & 4 Ewing (1978).

116

to the same Si, forming a chain of alternating edge-sharing Si0 tetrahedra and Th0 (Fig. 3b).

4 triangular dodecahedra extending parallel to c

8 These chains are joined in the a and b directions by

edge-sharing Th0 actually a

dodecahedra (Fig. 4b). The Si0 tetrahedron is 8 4 tetragonal disphenoid and it has a smaller O-Si-O angle

(101°) opposite the edge shared with the ThOB dodecahedron than that opposite the unshared-edge

(113.9°).

The Si-O bond length is 1.63A.

Each 0 is coordinated by one Si and two Th.

The silicate ion vibra-

tions in the Raman spectrum are of lower frequency in zircon than in thorite, indicating a relatively weaker Si-O bond in thorite (Syme 3 1977). The thorite structure has l4A voids centered on 3

et al' ~

which are connected parallel to c. Mumpton and Roy (1963) have

suggested that the zircon-like structures contain molecular water in these voids resulting in the composition AB0 ·XH 0. The chan4 2 nels may also serve as pathways for water entering the metamict material. Coffinite In their description of coffinite, Stieff et al. (1956) concluded that the x-ray diffraction powder studies indicated that coffinite is tetragonal and isostructural with thorite and zircon. Subsequently, Fuchs and Gebert (1958) reported oxygen positional parameters of

y

=

0.084(10) and

methods on hydrothermally 6.995A, c

=

6.263A.

a = 6.938A, c

=

z

= 0.222(10) obtained by powder

grown coffinite with lattice parameters a

=

Recently Nord (1977) examined a natural coffinite,

6.291A, with the transmission electron microscope and

found single-crystal

diffraction patterns consistent with tetragonal

symmetry. Huttonite Pabst (196lb) suggested that huttonite should be isostructural with monazite, CeP0 • The structure determinations of monazite that 4 have been done (Mooney, 1948; Veda, 1953; Mooney-Slater, 1962;. Chouse, 1965) are not in agreement.

The structure determination of huttonite 117

by Taylor and Ewing (1978) and the huttonite-group mineral cheralite by Finney and Rao (1967) differ in detail from each other and the monazite structur~s.

The huttonite used in the crystal structure

determination was a flux-grown crystal which has the space group P2l/n, S

=

Z

= 4, lattice parameters a = 6.784A,

104.9°.

b ~ 6.974A,

c = 6.500A,

The cheralite is a mineral with an intermediate composi-

tion in the REEP04-ThSi0 -CaTh(P0 )2 system. It has the space group 4 4 P2l/n, Z = 4, lattice parameters a = 6.7l7A, b = 6.920A, c = 6.434A, S = 103.8°. In huttonite Th is surrounded by 9 oxygcns

r

four "axial"

°

atoms at distances of 2.43-2.81A and 5 "equatorial" 0 atoms at distances of 2.40-2.58A (Fig. 2a).

In cheralite, the A atoms are bonded

to 8 oxygens at distances of 2.403 to 2.564A.

The 4 next nearest

oxygen atoms occur at distances of 2.778 to 3.945A; three are at distances of 3.154 to 3.945A; and pne, which is the ninth atom of Taylor and Ewing's (1978) Th0

group, is at a distance of 2.778A. In chera9 lite, Finney and Rao (1967) say that each of the four oxygens is bonded to three A-atoms and one B-atom, which is not consistent with an A0

polyhedron. 8 long (2.78-3.95A).

Two A-O bonds are short, 2.40-2.56A, and one is In huttonite, three oxygens are bonded to one Si

and two Th at distances of 2.40-2.52A, but one oxygen is bonded to one Si and three Th with the additional Th-O bond (2.81A) being much longer than the other two (2.50 and 2.58A).

The difference in des-

criptions of huttonite and cheralite appears to be a choice of what oxygens are included in the coordination polyhedron for the A-atom, there being at least 8 at 2.5A or less and perhaps one additional oxygen at a distance of ~ 2.8A. Similar to thorite, adjacent pairs of axial oxygens define edges on opposite sides of the Th0

polyhedra which are shared with Si0 9 4 groups and form chains of alternating Th0 and Si0 parallel to c 9 4 (Fig. 3a). The remaining five equatorial oxygens form a nearly (001)

planar pentagonal array around the Th atom. shared with other Si0

These oxygens are corner-

and Th09 groups (Fig. 4a). As in the case of 4 thorite, O-Si-O angles opposite shared edges in huttonite, ranging 118

from 99 to 104°, and O-P-O angles in cheralite (104°) are smaller than unshared edges in huttonite

(105-116°) and cheralite (106-114°).

As expected, the mean tetrahedral bond length for the Si0

tetra4 hedron in huttonite (1.62A) is larger than that (1.54A) for the P0

4

tetrahedron in cheralite. The huttonite structure forms a dense, space-filling network which, unlike the thorite-structure, water (Mooney-Slater, 1962).

cannot accomodate molecular

The structures of huttonite and chera-

lite are similar to one another and the monazite structures reported by Ueda (1953), Mooney (1948) and Mooney-Slater

(1962).

General actinide orthosilicate formula:

Table 2.

ABX4

B

X

Major:

Th, U4+, U6+

Si

0

Minor:

Fe3+, Ca

H. P

Trace:

Mn, Ti. Nb. Ta, Fe2+

A

Al, Pb, Be, Mg, Sn, Zr, Hf, Zn, Cu, Ce, La, Prj Eu, Gd, Tb, Dy, 'I'm, Yb, Lu , Y

Ge K, Na Nd, Sm Ho, Er

S. As B

F, CI (?) CO2 ( ?)

CHEMISTRY Forty-five elements have been reported as occurring in thorite, huttonite and coffinite, some of which may appear in various oxidation states (Table 2).

Most published analyses actually list compo-

sitions of bulk samples which are usually metamict and altered to secondary minerals.

In addition, several authors indicated that

other minerals were included as contaminants.

These factors make it

difficult to determine the actual compositions of the actinide orthosilicates and rationalize the chemical substitutions.

For these

reasons the crystal chemistry of the synthetic systems is important in understanding

the actinide orthosilicates.

Thorite

Substituents for thorium,

End-member thorite is ThSi(')4' Major

compositional variations involve the substitution of U, Fe, or rare 119

earth elements (REE) for Th.

U has been reported in amounts up to

about ZO wt. % U 0 (Robinson and Abbey, 1957), but this sample was 3 B suspected to contain uraninite as inclusions. A thorite with 15 wt. % U0

was found to contain thorian uraninite (Staatz et al.~ 1976). 3 4 6 Both U+ and U+ as UO and U0 have been reported in thorite analZ 3 yses, but total U is usually reported as either UO or U0 or U 0 , Z 3 3 B without regard to the true valence state of uranium. Fuchs and Gebert (195B) synthesized intermediate ThSi0 -USi0 solid solutions, 4 4 but Mumpton and Roy (1961) could synthesize thorite with no more than ZO to 30 mole % USi0 . 4 Although REE are generally limited to between 0.5 and 7 wt. %, they have been found in thorites in amounts up to ZO wt. % (Staatz et al.~ 1976).

Because of the metamict nature of the mineral and the

uncertain presence of contaminants, the mechanism of charge balance of REE+3 for Th+4 is unknown. For thorites with minor REE content, small amounts of P substituting for Si could provide a coupled substitution: REE+3+ p+5 ~ Th+4+ Si+4. In thorites with REE in much greater amounts than P, U+6 substitution could provide a mechanism for charge balance: +3 +6 +4 ... • +3 3+ ZREE + U t 3Th . In synthes1zed thor1tes w1th up to 1% Cd ,Er and Yb3+, electronic paramagnetic resonance (EPR) spectra of the REE's suggest that they occupy sites that have tetragonal and orthorhombic symmetries (Reynolds et al.~ 1972).

The tetragonal REE spectra are

assigned to REE ions substituting. at the tetragonal 4a site (Table 1) with the necessary charge compensation mechanism not disturbing the site symmetry.

The orthorhombic spectra of REE at higher REE concen-

trations is proposed to result from substitution of REE at the 4a site with a nearest-neighbor oxygen vacancy distorting the site symmetry. Thorite can apparently incorporate all REE's equally.

at.

Staatz et

(1976) found that of the REE present, yttrium and yttrium-group

lanthinides -- Gd, Dy, Er and Yb -- predominated in the thorites from the Seerie pegmatite, Colorado.

In their review of thorite analyses

from the literature that included the abundances of individual REE's, five analyses showed Ce as the most abundant REE and two contained abundant Nd. dominated.

In these seven thorites, the cerium-group lanthinides Two other thorite analyses were similar to the Seerie tho120

rites and were richer in yttrium-group lanthanides, except that Dy rather than Yb was the most abundant REE.

al.

From this data, Staatz et

(1976) concluded that thorite does not selectively accomodate

one group of REE's over another but rather incorporates whatever is available. The third major substituent is Fe and it is present in amounts up to 12 wt. % Fe 0 . Staatz et al. reported a metamict thorite with 2 3 5 wt. % Fe 0 containing small inclusions of goethite. Robinson and 2 3 Abbey (1957) report pyrite and magnetite as contaminants in an ironbearing thorite. The other elements which have been cited as substituting for Th (Table 2) are usually reported in amounts of 1 wt. % or less.

In

rare cases, amounts of up to 7 wt. % are reported. Any Pb present is believed to be radiogenic in origin.

is 2 Non-carbonate carbon

probably present in included carbonate minerals.

CO

may be present as microscopic films of hydrocarbon (Robinson and Abbey, 1957).

Calcium (up to 6 wt. % CaO) is reported to substitute

for U and Th in other minerals and may actually substitute for Th. high manganese-p1us-iron

thorite with ~ 13 wt. %

A

0 and 7 wt. % 2 3 (Krol, 1960) is believed to represent a mixture of thorite + Mn

Fe 0 2 3 Fe 0 + Mn 0 . Reported amounts of Zr and Hf could represent solid 2 3 2 3 solutions with zircon and hafnon. Mumpton and Roy (1961) found a miscibility gap on the ZrSi0 -ThSi0 join with a maximum of 6 mole % 4 4 ZrSi0 in thorite. A thorite with a high zr0 content of 1.5 wt. % 4 2 had a high Sn0 content of 3.6 wt. % (Heinrich, 1963). The thorite 2 was a stream sediment concentrate and may have contained zircon and cassiterite.

Substituents for silicon.

Chemical substitutions for silicon

have received more attention than those for thorium. thorite have been reported with up to 4 wt. % P20S

Analyses of and 2.1 wt. %

As 0 (Krol, 1962), up to 0.15 wt. % B 0 and up to 4.2 wt. % S. Sub2 5 2 3 stitution of p+S and As+5 for Si+4 would help in charge balancing the substitution of di- and trivalent cations for tetravalent thorium. However, the amounts present are much less than those needed to compensate for the amounts of Ca, Fe, and REE's reported in thorites. 121

/.,.1-

. ../'./ ......... / ..

/.:( :/ /

/./'

/

./'

Th(OH}4 Figure 5.

Compositions

stituents

of natural tborites plotted on a molecular

for TIl are not specified.

It 1s evident that

not of the type Th(Si04)I_x(OH)4x which would have compositions ThSi04-Th(OH)4' but lie

Water.

Up to 15 wt. % water has been reported

Controversy

tial, or water generally

are hydroxyl

(OH)x'

that the water

thorites

Dymkov

has arisen as to whether

that has been absorbed

accepted

(thorogummite)

and Nazarenko

with

the water

in thorite

the water is essen-

by metamict

is essential

Sub-

along

along the ThSi04-H20 join, indicating that water. After Mumpton and Roy (1961).

is present as molecular

analyses.

basis.

natural thorltes are

minerals.

It is

and that the minerals

the composition

(1962) have suggested

Th(Si0 )1_x 4 a complete solid

solution:

ThSi04 - Th(Si04)1_x(OH)4x - Th(OH)4 - Th02. Frondel (1953) reviewed the evidence for such substitutions, and Frondel

Collette

(1957) hydrothermally

preted as hydroxyl

thorite.

c 6.2BA) and more diffuse thorite sorption

(a

7.0BA,

Roy (1961) similarly

thorite,

Infrared

than higher

studies

which disappeared

(a 7.1BA,

cell dimensions

temperature

showed strong

with heating.

(OH) ab-

Mumpton

and

found that only well crystallized

duced above 400°C whereas dimensions.

at

str.ong. In a careful

p.olarized .optical abs.orpti.on study,

Hglenius

et al.

(1981; contra Faye et al., 1968) assigned the br.oad abs.orpti.on band at -1 2+ 3+ 3+ 2+ . . 16,300 cm t.o a Fe + Fe + Fe + Fe charge-transfer trans1t1.on in layer

11,

Tw.o bands

at 10,900

cm

-1

and 8,000

cm

-1

were assigned

unequivocally t.o spin-all.owed d-d transiti.ons in .octahedrally co.ordinated 2 Fe +, and the intensity .of the band at ~28,000 cm-l was related t.o 3 Fe + concentrati.on. They calculated eight highly c.orrelated (R > 99%) regression equations f.or band intensities as functi.ons .of the c.oncentra. 2+ 3+ . 2+ 3+ t1.ons .of Fe and Fe and the c.oncentrat1.on pr.oduct [Fe ][Fe ]. A n.ondestructive

'micr.osc.ope-spectr.oph.ot.ometric meth.od'related

t.o this w.ork was

rep.orted by H~lenius and 1anger (1980). It permits quantitative determi2 3 nation .of Fe + (t.o ± 0.15 g-at.om/l) and Fe + (t.o ± 0.05 g-at.om/l) .on chl.orit.oid grains

in thin secti.on with areal

resoluti.on .of ~lOµm.

Twinning "The twinning c.omp.ositi.onplane "Theoretically arrangement

.observed in chl.oritoid is always parallel

all twinning

in the immediate

comp.ositi.on plane

limited

i.e.

t.o a p.ositi.on where sheets

it must

on either

The darker

lines

similar

to that which

maintain

w.ould occur

Thus the comp.ositi.on plane in the untwinned

structure

side .of the c.omp.ositi.onplane

an

in Figure

la trace

if

in chl.orit.oid is the sequence

.of

is the same,

the cati.ons ... " in 1 .or l 1957, p. 81).

twin axes [010],

the

cleavage.

laws are p.ossible which

lie at the level.of

(Harris.on and Brindley,

with

neighb.ourh.o.od .of any at.om cl.ose t.o the

essentially

n.ormal gr.owth t.o.okplace.

atomic

t.o the basal

lamellar

12

the directi.ons .of permissible

in 11: [100], [130], [l}O]; in 12 (Fig. lb) they trace [110], [lIO]. As Harris.on and Brindley p.ointed .out, [130]I[l}0] 166

and

[110]\[110]

are symmetry-related

C2/c chl.orit.oids, leaving

and

.only [100],

have been .observed experimentally. chl.orit.oids. [210] and

Hietanen

[310].

p.ossible because

[130] and

[110], all .of which

P.ossibilities

(1951) listed

Fr.om Figure

[010] is the tw.o-f.old qxis in

are wider

in C1

three .other twin axes:

1 it is clear

.of the pseud.o-hexag.onal

[120],

that these and .others are

cl.osest-packed

nature

of this

structure. DEHYDRATION

AND STABILITY

T.op.otactic Dehydrati.on-Oxidati.on Bachmann takes

place

(1956) pr.op.osed that dehydrati.on

in air .of chl.orit.oid

acc.ording t.o the reacti.on [using structural

f.ormulas]:

[Fe;+Al0 (OH)4]-1[A1 0 ]-7[Si ]+8 + 2 3 8 2 3+ -1 -7 +8 [Fe2 Al0 ] [A1 0 ] [Si ] + 2H 0. 4 3 8 2 2 He observed

that the spacing

n.ormal t.o (001) increased

layer

in tw.o-layer chl.orit.oid (p.ossibly 2M ?) l described as a single-layer defect structure.

p. 90) questi.oned his experiment, suggested 1962)

his experiment

under

characterizati.on

n.o change

(black-brown)

Halferdahl

(1961,

(Fig. 37, p. 164 in Deer et al.,

but n.ot in detail.

The latter

m.ore contr.olled c.onditi.ons and with

.of their

In vacuo f.or several with

t.o 9.36 A in what he

and Jeffers.on and Th.omas (1979)

that his pr.op.osed structure

was c.orrect in essence

fr.om 8.9 A per

starting

repeated

careful

pr.oduct.

h.ours at 700°C,

2M2 chl.oritoid dehydrated

in m.orph.ol.ogyt.o a c.ompletely am.orph.ous, nearly mass with n.o evidence

of crystallinity

visible

opaque

even at

the highest

res.oluti.on .of the electr.on micr.osc.ope.

temperature

the same c.ol.orand m.orph.ology were .observed, but the de-

hydrated,

t.opotactically

three-layer, Thomas

.oxidized pr.oduct is a distinctly

rh.omb.ohedral structure.

(1979),

In air at the same

Designated

it has cell dimensi.ons a

=

5.8, c

crystalline,

3R by Jeffers.on and

=

28 A.

The .oxygens

and Al at.oms .of layer

L2, the Si at.oms and the ir.on at.oms .of Ll are

essentially

in p.ositi.on, but the ani.ons .of Ll are rearranged

unchanged

t.o f.orm a 3-f.old array (their

Fig.

.of symmetrically

equivalent

[Fe3+0 ] s

p.olyhedra

7b).

At relatively

rapid

heating

rates 167

(> 2.soC/min),

van der Plas

et al. (1958)

rep.orted an endothermic

as seen in TGA and DTA pl.ots. 10SO°C.

Frans.olet

(1978)

C/min his specimen and complete

reaction

All the water

reviewed

.off until

the data f.or .ottrelites:

sh.owed an end.othermic

dehydrati.on

in chl.orit.oid at 770°C, was n.ot driven

reacti.on between

at 10°

670 and 770°C

by 820°C.

Stability Because grades

it is an imp.ortant marker

.of metam.orphism

the subject since

(Winkler,

.of numer.ous experimental

the devel.opment

limits

pressure

(10 - 25 kbar)

t.o the c.oexisting minerals

r.ocks (Ganguly,

tions .of chl.oritoid (1970, 1974) kbar water evidence gested

buffers.

his .own, up t.o 1961.

1969),

pressure

The papers

Halferdahl

stability

.of high

.oxygen

of its stability

.of the reacti.on rela-

1972).

Grieve

and Fawcett's

.of chl.orit.oid below

am.ong .other imp.ortant data,

is n.ot a "stress

reviews

.of regi.onally metam.orph.osed

.of the stability

yielded,

that chlorit.oid by Harker

(Albee,

particularly

and relatively

and by a study

and staur.olite

investigati.on

been

The next maj.or w.ork was

This was foll.owed by an investigati.on

relative

pelitic

investigati.ons,

and Newt.on (1968) .on the thermal

chl.orit.oid at high fugacity.

in the l.ow and middle

chl.orit.oid has recently

.of .oxygen fugacity

all the w.ork, including that of Ganguly

mineral

1965),

mineral,"

10

c.onclusive

as had been

sug-

(1932). .on .occurrences

and parageneses

.of chlorit.oid are t.o.o

numer.ous t.o menti.on and are in any case bey.ond the sc.ope .of this w.ork. See Halferdahl

(1961)

w.orks .on stability ences.

f.or an imp.ortant review

and the af.orementi.oned

and reacti.on relati.ons for later

Li.ou and Chen's

(1978) recent

work

many .of the imp.ortant petr.ol.ogic studies. Baltatzis

(1980),

H.oldaway

(1978),

Frans.olet

(1978) has summarized

See als.o Athert.on

and Cruickshank

studies

168

imp.ortant refer-

c.ontains references

and Ghent

.of the Mn-rich

t.o (1980), (1978);

chl.orit.oids.

CHLORITOID:

REFERENCES

Albee, A.L. (1972) Metam.orphism .of pelitic schists: reaction t Lons o f ch l.o r t t.o Ld and staur.olite. Ge.ol. So c , Am. Bull., 3249-3268.

rela83,

Athert.on, M.P. (1980) The occurrence and implicati.ons .of chl.oritoid in a c.ontact aure.ole and alusite schist fr.om Ardara, C.ounty D.onegal. J. Earth Sci. R. Dublin S.oc., 3, 101-109. Bachmann, logr.,

H.G. v.on (1956) Dehydrati.on v.on Chlorit.oiden. 108, 145-156.

Z. Kristal-

Baltatzis, E. (1980) Chl.orit.oid-f.orming reacti.on in the eastern Sc.ottish Dalradian: a p.ossibility. N. Jahrb. Mineral. Mh., 1980, 306-313. Bethune, Bull.

P. (de) (1977) La c.omp.ositi.onchimique Soc. beIge Ge.ol. 86, 9-11.

des chl.oritoides belges.

Beugnies, A. (1976) Structure et metam.orphisme du pale.oz.oique de la regi.on de Muno, un secteurclef du d.omaine hercyniende 1 'Ardenne. Ann. Mines Belgique, 6e livraison, 481-509. Brindley, G.W. and F.W. Harris.on (1952) The structure Acta Crystall.ogr., 5, 698-699.

.of chl.orit.oid.

Cruickshank, R.D. and E.D. Ghent (1978) Chl.oritoid-bearing pelitic .of the H.orsethief Creek Gr.oup, s.outheastern British C.olumbia. Contrib. Mineral. Petr.ol., 65, 333-339. Deer, W.A., V.ol. 1.

R.A. H.owie and J. Zussman (1962) Rock-Forming L.ongmans, Lond.on. pp. 161-170.

r.ocks

MineraZs,

D.onnay, J.D.H., W. Nowacki and G. D.onnay (1954) Crystal Data. Ge.ol. S.oc. Am., 60, 138.

Mem.

Faye, G.H., P.G. Manning and E.H. Nickel (1968) The p.olarized .optical absorpti.on spectra .of t.ourmaline, c.ordierite, chl.oritoid and vivianite: ferr.ous-ferric electr.onic interacti.on as a s.ource .of pleochr.oism. Am. Mineral., 53, 1174-1201. Frans.olet, A.M. (1978) D.onnes n.ouvelles sur l'.ottrelite d'Ottre, Belgique. Bull Mineral., 101, 548-557. Ganguly, J. (1969) Chlorit.oid stability and related parageneses: The.ory, experiments, and applicati.ons. Am. J. Sci., 267, 910-944. ----- and R.C. Newt.on (1968) Thermal stability .of chl.orit.oid at high pressure and relatively high .oxygen fugacity. J. Petrol., 9,444446. Grieve, R.A.F. and J.J. Fawcett (1970) The synthesis l.ow pressures. Am. Mineral., 55, 49-135. ----- and ----- (1974) The stability J. Petr.ol., IS, 113-139.

.of chl.orit.oid at

.of chl.oritoid bel.ow 10 kb PH20.

H~lenius, U., H. Annersten and K. Langer (1981) Spectr.osc.opic studies .on natural chl.orit.oids. Phys. Chem. Minerals, 7, 117-123. ----and K. Langer (1980) Micr.osc.ope-ph.otometric meth.ods f.or non-destructive Fe2+-Fe3+ determinati.ons in chl.orit.oids (Fe2+,Mn2+,Mg)2(Al,Fe3+)4 Si2010(OH)4. Lith.os, 13, 291-294. 169

Hansc.om, R.H. (1973) The Crystal Ph.D. Dissertati.on, Harvard

Chemistry Univ.,

and Polymorphism

Cambridge

of Chloritoid.

Massachusetts.

---

(1975) Refinement .of the crystal structure chl.orit.oid. Acta Crystall.ogr., B3l, 780-784.

---

(1980) The structure .of triclinic chl.orit.oid and chl.orit.oid p.olym.orphism. Am. Mineral., 65, 534-539.

Harker,

A.

(1932) Metamorphism.

Methuen,

.of m.on.oclinic

L.ond.on.

Harris.on, G.W. and G.W. Brindley (1957) The crystal chl.oritoid. Acta Crystall.ogr., 10, 77-82. Hietanen, A. (1951) Ch.orit.oid fr.om Rawlinsville, Pennsylvania. Am. Mineral., 36, 859-868.

structure

Lancaster

.of

C.ounty,

H.oldaway, M.J. (1978) Significance .of chl.orit.oid-bearing and staur.olitebearing r.ocks in the Picuris Range, New Mexic.o. Ge.ol. S.oc. Am. Bull., 89, 1404-1414. Jeffers.on, D.A. and J.M. Th.omas (1977) Structural t o Ld , E.C.M.-4 Pro c . (Oxfo rd ) , 626-628. ---

variation

in chl.ori-

and --(1978) High res.oluti.on electr.on micr.osc.opic and X-ray studies .of n.on-rand.om dis.ordered in an unusual layered silicate (chl.orit.oid). Proc. R.oy. S.oc. L.ond. A., 361, 399-411.

Jeffers.on, D.A. and J.M. Th.omas (1979) T.op.otactical dehydrati.on .of chl.oritoid. Acta Crystall.ogr., A3s, 416-421. Kramm, U. (1973) Chl.orit.oid stability in manganese rich l.ow-grade metam.orphic r.ocks, Venn-Stavelot Massif, Andennes. C.ontrib. Mineral. Petr.ol., 41, 179-196. Li.ou, J.G. and P.-Y. Chen (1978) Chemistry and .origin .of chl.orit.oid r.ocks fr.om eastern Taiwan. Lith.os, 11, 175-187. Plas, L. van der, T. HUgi, M.H. Mladeck and E. Niggli (1958) Chl.oritoid v.om Hennensadel sUdlich Vals (nordliche Aduladecke). Schweiz. min. petr.ogr. Mitt., 38, 237-246. R.oss, M., H. Takeda and D.R. W.ones (1966) Mica p.olytypes: descripti.on and identificati.on. Science, 151, 191-193.

Systematic

Tricker, M.J., D.A. Jefferson, J.M. Th.omas, P.G. Manning and C.J. Elli.ott (1978) Mossbauer and analytical electr.on micr.osc.opic studies of an unusual orth.osilicate: chl.orit.oid. J. Chem. S.oc., Faraday Trans. II, 74, 174-181. Winkler, H.G.F. (1965) Die Genese der metamorphen Verlag, Heidelberg.

170

Gesteine.

Springer-

Chapter 7 P. H. Ribbe

STAUROLITE INTRODUCTION Other than a recently origin"

(Gibson,

medium-grade

1975), staurolite

regionally

therefrom.

Inasmuch

staurolite

does not address

about the exact chemical

1

investigations studies.l

petrologic

composition

of

to footnote

to experimental

field-related

derived

the subject

reader is referred

relating

igneous

found in

rocks and in sediments

the interested

and major recent

Uncertainties

"of undoubted

is almost exclusively

metamorphosed

list of references

of its stability

occurrence

as this chapter

paragenesis,

for a selected

discovered

of staurolite

confusion

the H20 content and the valence state(s) of iron - and about the space group and thus the crystal structure have

persisted

until very recently.

-

in particular

mined

that the structure

array

of (O,OH) anions,

four partially

occupied

HSFe4Al16SiS04S·

For example, Naray-Szabo

of staurolite but refining octahedral

(1929) deter-

was based on a closest

packed

in space group Ccmm, he overlooked

sites and suggested

On the basis of six wet chemical

a formula

analyses

of

Juurinen

(1956) postulated

an incorrectly balanced formula H4Fe4AllSSiS04S' 2+ (1972) gave Fe4 AllSSiS046(OH)2 as "the idealized stoi-

but Ganguly chiometry

of staurolite,

at least as a limiting

formula

had been suggested

augural

dissertation

hydrogens,

was essentially

ment of the structure

in 1915 by Horner

and, except

composition."

in his unpublished

for the exact number

affirmed

by NaraY-Szab6

This

in the more nearly and Sasvari

in-

of cations correct

and

refine-

(1958; discussed

below). With

the advent

site refinements lExperimental

of more precise

of the crystal

chemical

structure

analyses,

least-squares

using both x-ray and neutron

investigations:

Hoschek (1967,1968), Schreyer and Seifert Field-related

Richardson (1968), Ganguly and Newton (1965), (1969), Ganguly (1972), Hellman and Green (1979), Yardley (19S1). petrologic studies:

Chinner (1967), Schreyer and Chinner (1966), Hietanen (1969), Hollister (1969), Guidotti (1970), Albee (1972), Kwak (1974), Smellie (1974), Ashworth (1975), Gibson (197S). A book entitled "Staurolite" by V.V. Fed'kin (1975, Moscow: Academia Nauk USSR, 272 pp.) contains much crystal chemical data and detailed discussions of staurolite parageneses in context of occurrences in the USSR. 171

x ~

=Oxygen at z-O and_O-S

Figure 1. lustrated (modified epitaxial Switzerland his Figs.

0- Oxygen

at z-0-2S

and -

0-75

The structure of staurolite projected on (001). Two unit cells are iland the kyan1te portion of the structure is outlined by dashed lines from Naray-Szab6 and Sasvari (1958, Fig. 3, p. 863). Wenk (1980) studied intergrowths of staurolite and kyanite in specimens from Al.pe Sponda, and found the interface to be coherent with a few dislocations (see 1 and 2).

Figure 2. Schematic drawing of the AlO.7Fe202 (OR) 2 layer of staurolite showing arrangement of Fe tetrahedra and Al octahedra. Approximate site occupancies as determined by Smith (1968) in a specimen from St. Gotthard are indicated by filled portions of circles: see text for details. Modified from Dickson and Smith (1976, Fig. 7, p , 214).

172

diffraction

data, Mossbauer

and valence, teractions

between

the structure stood.

spectroscopic

and nuclear magnetic

studies of dipole-dipole inspins of paramagnetic Fe2+, both

H+ and the electron

and the chemistry

The generalized

studies of iron distribution

resonance

of staurolite

structural

formula

are now fairly well under-

suggested

by Smith

[7 octahedral

sites, principally

[1 tetrahedral

site, principally

Fe]4 or

2 for chondrodite,

3 manganhumite,

has been synthesized. pers. comm.)

°


'=14.3

1

1

13-9

I

I

13,3

4-1

1·720 1·700 1·680 1·660 1·640

I

~ ~....q >1 I?AI

I d~

7'

p.::;8+t====1 I ~ 0 10 Forsterite

Figure fayalite

30

I

Hyalosiderite

I

Horronolite

40

50

60

Atomic per cent. Fe+2

I 70

Ferrohortonolite 80

305

3.7 3'5

90 100 Fayalite

14. Variation of refractive indices, 2V, and density with for the Mg-Fe olivine series. (From Deer et al.., 1966).

mol

crys-

(1980) who

R.l. )·860

to

%

claim that they are accurate greater

to ~2% Fa (correlation

coefficients

are

than 0.999): mole % Fa = (n

- 1.6325)/0.0020

ex

mole % Fa = (n mole % Fa where n , nQ' and n ex

Similar

µ

equations

=

are the indices of refraction

y

with refractive

also derived by Laskowski

1.6361

+

nS

=

1.6473

n

=

1.6694

+ +

ex

Y

they employed

Obviously,

as dependent

+

~a 0.00159 ~a 0.00116 ~

0.00001

were

X;a

+

a

0.00001

X2 Fa

together with the dispersion

compositions

1963),permit

on unaltered

Ca and Mn substitution

significant

variable

+ 0.000006 xia

(see Grabar and Principe,

of olivine

for sodium D light.

and are as follows:

0.0011

They claim that these equations,

termination

indices

and Scotford

=

n

method

- 1.6490)/0.0022 S (n - 1.6651)/0.0022 Y

staining optical

de-

grains in thin section.

will affect the utility

of

this method. The optical properties tephroite Pawson

properties.

Both studies

nomograph

Hurlbut

Theoretical

(1957) and Mossman

and

the effect of Ca on optical the compositional

dependence

index and the d130 spacing of olivine in a compo(see Fig. 6) which they claim is accurate to ~2 mol

(1961) also correlated

the forsterite-tephroite

fayalite

considered

The more recent study combines

of the nS refractive

% Fo.

from the forsterite-fayalite-

series have been studied by Henriques

(1976).

sitional

of olivines

nS and d

130

aspects of the optical properties

crystalline

with composition

for

series.

solution

series are discussed

of the forsteriteby Hauser

and Wenk

(1976) . Density The relationship fayalite

between

density

series has been studied by Bloss

p. 349) and by Fisher and Medaris based on measurements XFa ,~Bloss,

and composition

(1969).

for the forsterite-

(1952) (see also Bloss, 1971'~ Bloss' regression

of natural

samples,

=

+ 47.6852 P + 5.25529 p

-207.754

is:

F .D. (1971) Cryetallography and Crystal Chemietf'y, an Introductrion; Holt, Rinehart and Winston, 545 pp-

306

equation,

2

New York:

and the Fisher-Medaris

=

P In these equations Both studies

equation

~a

olivines

is:

2 4.4048 - 1.1353 XFa - 0.0435 X Fa is the mole percent

found that the relationship

is consistent

with

The variation

of density with

in Figure

for synthetic

ideal behavior

and p is density.

fayalite

between

density

and composition

of the forsterite-fayalite

composition

series.

for the Mg-Fe olivines

is shown

14.

Unit Cell Parameters Numerous

studies

have been made over the past 30 years of the varia-

tion of cell parameters

along different

vine group of minerals.

compositional

The most notable

Henriques

(1957) [Mg2Si04-Fe2Si04-MnSi04];

LiMgP04);

Fisher

(1967), Louisnathan

(1968), Fisher and Medaris

joins for the oli-

of these include

et al. (1966) [Mg Si0 -

Bradley

and Smith

and Weiss

(1978) [Mg2Si04-Fe2Si04];

Matsui

2 4 and Syono

(1968), Matsui

(1969), Schwab and Kustner

Ca2Si04];

studies by

(1977), and Riekel

Wyderko and Mazanek (1968) [Fe Si0 2 4 (1968) [Mg2Si0 -Co2Si0 and Mg Si0 -Ni Si0 ]; 4 4 2 4 2 4 Nishizawa and Matsui (1972) [Mg2Si04-Mn Si0 ]; Syono et al. (1971) 2 4 [Mg2Si04-Zn2Si04 at pressures ranging from 70 to 90 kbar at l200°C]; and Warner and Luth (1973) [Mg2Si0 -MgCaSi0 ]. 4 4 A number of studies have also correlated d with composition for 130 the forsterite-fayalite series (Yoder and Sahama, 1957; Fisher and Medaris,

and Syono

1969; Schwab and Kustner,

Schwab and Kustner

relating

1977).

mole fraction

The regression fayalite

(~a)

equation to d

130

of (in A)

is: XFa

=

7.522 - 14.9071

For the forsterite-fayalite

the variations

V, and d130 show slightly and Kustner, 1977; Fisher

positive

cism because

by Riekel and Weiss

of significant

and the general

concensus

particularly

1/2 of b with

compo-

of a, c, and unit cell volume, from linearity

1969).

(Schwab

The report of distinct

in slope in plots of a, b, c, and V versus

series reported

series,

the variation

deviations

and Medaris,

)

130

series,

sition is linear, whereas

breaks

(3.0199 - d

composition

for this

(1978) must be viewed with skepti-

differences

between

values reported

the high precision 307

their cell parameters

by all other workers

for this

data of Schwab and Kustner

(1977).

024

306

VIA') J302 ~298

..,

-1294 --'290

o

25

50

75

100

Mn.$1o. mol·..

M;.SiO.

o

Mn,SiO.

25

MQ.Sic,

50

Fe,SiO.

75

(b I (Mg ,Fe)2

478~--

,

alA) ~

-_,-------

(

~

,028

."~

r

4.72 -I

b

a

474

/1~I030

'

olivine

all)

,: ~

bill

SIO.

-,

a

476' 1030

100 Fe,SiC,

mol %

bill

'1'°

28

"-

10,20

bll)

10,26

10,18

1024

10,16

'026 1024

·

10,22

1022

.~I,020

V

.>

60

Cll)

c

600 5,9

0,12

1020

..

296

VII') 294 292 282

290 j

~ Zn,Sio. (el

75

50

mol %

(Mq.Zn).Siq,

"".in'

0~--~2~5---'5~0~~~~--~'00

100

MliJaSiO.

Zn,SiQ, (d)

«Mq. Co'2 Si ~ Olivlne

(e)

Ni.SiO.

m~

(M9,Ni"

Si~

%

Ni.sio.

olivine

Figure 15. Variation in unit cell parameters for fiye olivine crystalline solution series involving Mg. (From Akimoto et aZ., 1976). JOB

of a,

The variation for the crystalline

b, c,

solution

and Vwith

series

composition

(Mg,Mn)2Si04'

(in mole percent)

(Mg,Fe)2Si04'

(Mg,Zn)2

Si04, (Mg,Co)2Si04' and (Mg,Ni)2Si04 are shown in Figure 15. Significant curvature is seen in all plots but the one for the (Mg,Fe)2Si04 series, indicating

that Vegard's

The non-ideal

mixing

of octahedral

cations

law is violated

indicated

an excellent

and the size of cations

tahedral

sites of olivine.

silicate

olivines

Figure

covering

In preparing

This

in detail in a later section.

As might be expected,

samples.

solutions.

to the ordering

in the M(l) and M(2) sites in these olivines.

subject will be discussed

cell volume

in these crystalline

by these data is related

correlation

(expressed

exists between unit 3 in A ) occupying the oc-

16 illustrates

this correlation

the entire composition

this plot, Brown

for

range shown by natural

(1970) used the cell parameters

of Smith et al. (1965) for Ca2Si0 . These values have since been re4 vised by Czaya (1971), although the figure has not been redrafted to include

this revision.

is 385.3 A3. to cations

The corrected

Brown's

regression

radius cubed

volume

for pure calcio-olivine

equation which

(using Shannon

3 rM

V = 188.32

relates unit cell volume

and Prewitt

+

.MgCo

310.0.

... MnCo x

300.0

(Fe5Co4Mq,),

+Mn,

* FeMn

290.0 280.0

LL .30.

.40

,50

,60

.70

,80

.90.

1.0.0.

r,; ($,3) Figure 16. Variation of unit cell volume (A3) with cation radius were taken from Shannon and Prewitt (1969). (From Brown, 1970). Table 4. Cell

Parameters

Olivine Mg2S104 Fe2S104

of End-Member Ollvlnes

cubed.

Radii values

at 24 C and 1 Atm. Pressure'" Q

u&

£_ill_

-"--.ill

.u0.

4.7540{Z)

1O.1971(8)

5.9806(6)

289.92(6)

Schwab and Kustner

(1977)

4.8Z11(5)

10.4779(7)

6.0889(5)

307.58(8)

Schwab and Kustner

(1977)

Reference

Hn2Si04

4.904

(1)

10.601

(3)

6.259

(I)

325.4

Ca2Si04

5.078

(Z)

11. 225 (3)

6.760

(2)

385.3

Ni2Si04

4.7274 (5)

10.118

5.9105(8)

282.7

Co2Si04

4.7811 (7)

10.2998(9)

6.0004(4)

295.49(5)

(Mg.5 Fe.5 )2S104 (Mg.5 Mn.5 )ZS104

4. 79Z9(Z)

10.341Z(3)

6.0380(2)

299.27(3)

Schwab and Kustner

4.818

10.447

6.130

308.5

Nishizawa

(Mg.48Ni. 5Z) ZS104

4.7366(4)

(Mg.5 Zn.5' )Z5104 {Mg.5 Ca.5 )ZSi04 (Fe. 51Mn.47Mg.OZ)ZS104

4. 8Z09(5) 4.844

(Fe. 49Ca• 51) ZS104

4.892

Ca.5 )ZS104

4.944

(Mo.5

*Numbers 1n parentheses

4.775

(1)

(1)

(3)

(Z)

10.1716(13) 10.250

(3)

(1)

5.9374 (4) ~.994

(2)

(2)

(I)

(I)

286.06(4) 293.3

Nishizawa

and Matsui

(3)

Brown (1970) Brown (1970)

5yono et al.

(I)

10.577

(4)

6.146

(2)

314.9

(2)

Brown (1970)

(5)

11.180

(2)

6.469

(4)

353.8

(4)

Brown (1970)

(4)

11.190

(10)

6.529

(5)

361. 2 (5)

standard errors

310

(1 0) and refer

(1972)

Rajamani et al., (1975)

6.37Z6(6)

340.74(4)

(1977)

and Matsui

11.0911(9)

are estimated

(1972)

Czaya (1971)

(1971)

Warner and Luth (1973)

Caron et al , (1965)

to the last

decimal place.

UNIT CELL VOLUME ($..3) 280..0

290.,0.

300.0

310.0

320.,0.

330.0

340.,0.

350..0

360.0.

370,0.

380.,0.

390.,0. 40.0,0.

2.42

Co /

•

2,38

o

Co

2,34 ~

2,30.

~

Kio

6.

2,26

o

OMo

I

~

2,22

V 2,18 2.14 2.10. ,72

,76

,80

,84

,88

,92

,96

1.0.0

1.04

1,0.8

1,12

1.16 0.,20.

1.24

1.28

rM ($..) Figure 17. Variation of mean M-Odistance with mean octahedral unit cell volume, V. Abbreviations for mineral names and values in Table Al. (From Brown, 1970).

cation radius, r , and of r and V are M given M

2.24 2.23

Zn-Py'

,,7-

2.22 2,18

2.21

2.17

2.20

2,16

B

2.19 A

0

2.15

I

2.18

i

2,17

ru.

2.14 r-;

V

o d:.

2,13

i

2,12

2.15

2.11

2.14

Ho

2.16

/

V

2.10

/

2.12

2.08

2.11

2.07

2.10

2.06

0

7

2.13

2.09

/~

x Observed Disordered

.:

o

• Ordered

2.09

70

71

.72

73

74

75

.76

,77

.78

.79

.80

70

rMm

71

.72

.73

,74

75

76

,77

78

.79

.80

r"(21

Figure 18. Variation of mean M(l)-O (A) and M(2)-0 (B) distances with calculated radius of M(l) and M(2) cations for non-calcium olivines. Data for this plot are contained in Tables Al, A3, and A4 in appendix. (From Brown, 1970).

311

81

82

MM

M

~ '"

0'1 ,....

~,....,....

co

_O\--_O\~ ~---,....-c

0"1

c_________

-0\0'10"10\0'10'10'10'10\

C

0'10"10\

-~~~-o~~~

__

_ ""',....MM __ 0'1 0\ 0'10'\

r-..,....,

,....,....,....

---

0'\0'\0'10\

u


2,"',

r

'0

'------

I

N;

212

Aoo

200

800

600

1000 2.10,

TOC

1------

1

1---------

AOO

200

---

600

800

1000

TOC Figure 26~. Plots of mean M(l)-O and M(2)-O distances ver8US olivines listed in Table 6. (From Lager and Meagher. 1978).

than in forsterite parameters

for fayalite.

cal properties to dictate

structure,

and they probably

are weaker

melting

the M-O bonds are the weakest

break before

the stronger

of physibonds tend

point, etc.

cation-oxygen

In

bonds,

Si-O bonds at the melting

that the longer Fe-O bonds in

than the shorter Mg-O bonds

that all other factors

dependence

is that the weakest

such as hardness,

If we make the gross assumption

fayalite assume

and composition

properties

for the six

itself in larger unit cell

A rule of thumb concerning

on structure

physical

the olivine

point.

(2.114 A), which manifests

temperature

are essentially

likely not the case), then the lower melting

in forsterite,

and further

the same (which is most point of fayalite

can be

rationalized. A more satisfying recently

presented

and M-O distances

structural

by Hazen

rationalization

of olivine melting

(1977 ) who extrapolated

of ferromagnesian

olivines

was

the cell parameters

to their melting

points and

found that they all have similar cell parameters (a = 4.89, b= 10.6, c = 3 (V ~ 319 A ), (2.19 A) and (2.22 A)

6.19 A), cell volume

323

distances

at their respective

concluded

that the solidus of ferromagnesian

structural

line above which olivine

with respect sitions).

melting

to a more Fe-rich

Hazen speculated

that "perhaps

occupies

due to misfit

the solidus

structure

olivines."

the M(2) site.

in olivines

compo-

of expanding

represents

It is interesting olivines

at room temperature

Both 'the

Hazen an iso-

is not stable

(except at end-member

limits for ferromagnesian

point are exceeded

represents

of a given composition

limit for ferromagnesian

that these upper distance melting

(see Fig. 24).

olivines

olivine melt

tahedra with rigid tetrahedra, structural

temperatures

and

oc-

a critical to note

at their

only when Ca

distances

in

Ca2Si04 exceed these limits yet the silicon tetrahedron is of the same dimensions in this structure as in all other silicate olivines. Following Hazen's

reasoning,

one might

to the rarity of calcio-olivine mismatch

between

"overstuffed" lations

speculate

in nature

that a contributing

is the apparent

the rigid, small tetrahedron,

Ca octahedra.

However,

and the more pliable,

we cannot consider

to be anything but manifestations

factor

dimensional

these specu-

of more fundamental

physical

reasons.

Ca2Si04 polymorphism. changes at low pressures Ca2Si04 undergoes

The common olivines before

they melt.

undergo no polymorphic

However,

a complex series, of structural

the calcio-olivine

changes before melting

as is shown below:

The calcio-olivine literature. of labeling

structure

This practice

the lowest temperature

ature polymorph

S, etc.

is given the Greek prefix y in most

does not follow the standard polymorph

Furthermore,

flicts with the usage of the prefixes the geophysical dicates

literature

the olivine

a, the next highest

this system of nomenclature a and y' in this chapter

where y indicates

tempercon-

and in

the spinel phase and a in-

the S-form of Ca2Si04, is metastably formed as the a' phase is cooled below about 700°C because of the closer structural

similarity

phase.

U. S. convention

Larnite,

between

the a' and S forms than between 324

the a' and

y forms

(Smith et al., 1965).

table S form is fortunate

This metastable

the S phase must be preserved when

the S phas·e reverts

inert and constitutes Eysel and Hahn polymorphism. includes

persistence

of the hydra-

for all of us in a very practical in the manufacturing

to the olivine

of cement clinker;

form in this clinker,

it is quite

a failure. (1970) present

a lucid review of Ca2Si04 and Ca2Ge04 on the polymorphism of Ca2Si04 (1950), Foster (1968), Forest (1971), Kazak et

Other pertinent

papers by Bredig

literature

al., (1975), and Ghosh et al., (1979).

The last paper places

the uses of Ca Si04 polymorphs in the cement industry. 2 As pointed out in an earlier section on minor element calcio-olivine,

sense because

larnite

(S-phase),

and bredigite

emphasis

on

chemistry,

(a' phase)

can coexist

in nature. Structural

Response

Considerably the olivine

because

experiments

high pressure

are typically

than room Dr high-temperature

pressure

cells developed

U. S. have permitted forsterite

(Hazen, 1976:

In addition,

for forsterite

Nonetheless,

the effects

1974) and synthetic

fayalite

of pressure

labs in the

(Hazen, 1977a:

on the cell param-

fayalite

(Yagiet

The high-pressure

are listed in Tables

£ill..

£ill.

b(A)

al., 1975; cell parameters

7 and 8, respectively.

289.80(5)

(1)

,5.954 (6)

285.0 (5)

10.02

(1)

.5.940 (6)

281.8 (5)

9.97

(1)

5.955 (6)

279.7 (5)

10.19

(1)

5.980 (6)

289.5 (5)

4.7535(4)

10.1943(5)

20 kbar

4.743 (5)

10.09

40 kbar

4.734 (5)

50 kbar

4.712 (5)

After

4.749 (5) high pressure

V(p)

5.9807(4)

1 atm.

1 atm.*

high

data to be taken for synthetic

Table 7. Forsterite (Fo100) unit cell parameters at different pressures (T • 23·C). Numbers in parentheses are standard errors referring to the last decimal place. (From Hazen, 1976).

z

more dif-

(Olinger and Duba, 1971; Schock et al., 1972;

1931) were determined. and fayalite

on

x-ray or

an order of magnitude

50 kbar) and synthetic

peridot

and Halleck,

single-crystal

experiments.

structural

31 and 42 kbar).

also see Adams,

of pressure

during the past decade at various

olivine

eters of powdered Olinger

Changes

less work has been done on the effects

structure

spectroscopic ficult

to Pressure

experiments.

325

Table 8. FayaUte (FalOO) unit cell parameters at different pressures (T - 23°C). Numbers in parentheses are standard errors referring to last decimal place. (From Yagi et az', 1975).

p

Fe2SiO. olivine

(kbar)

vivo

V 3 (A )

0 19 33 44 53 23 42 60 71 29 47 61 73 62

a

307.9(7) 303.2(15) 300.5(3) 297.9(11) 296.7(10) 301.5(23) 298.5(19) 295.7(7) 293.0(15) 30[,6(15) 296.7(25) 294.7(16) 292.5(17) 293.8(16)

[,0000 0,9848 0.9761 0.9678 0.9638 0.9793 0.9696 0.9604 0.9518 0.9796 0.9637 0.9572 0.9500 0.9543

discrepancies

b/bo

b

[,0000 0,9977 0.9905 0.9907 0.9915 0.9971 0.9940 0.9900 0.9886 0.9936 0.9956 0.9902 0.9861 0.9896

in obtaining exist between

c/co

c

(A)

4.817(6) 4.806(8) 4.771(1) 4.772(6) 4.776(5) 4.803(13) 4.788(10) 4.769(4) 4.762(8) 4.786(8) 4.796(14) 4.770(9) 4.750(9) 4.767(8)

In view of the difficulty that major

0/00.

(A)

(A)

10.49(1) 10.43(2) 10,37(1) 10.33(1) 10.31(1) 10.36(2) 10.32(2) 10.28(1) 10.25(2) 10.38(2) 10.29(3) 10.26(2) 10.23(2) 10.25(2)

[,0000 0.9934 0.9881 0.9847 0.9824 0.9875 0.9838 0.9798 0.9764 0.9892 0.9807 0.9772 0.9746 0.9767

6.091(8) 6.052(11 ) 6.073(2) 6.042(8) 6.026(7) 6.057(17) 6.038(14) 6.030(5) 6.005(11) 6.071(11) 6.011(18) 6.024(12) 6.020(13) 6.012(10)

[,0000 0.9936 0.9970 0.9920 0.9893 0.9944 0.9913 0.9900 0.9859 0.9967 0.9869 0.9890 0.9883 0.9870

these data, it is not surprising fayalite

cell parameters

of Yagi

et al. (1975) (taken at 44 kbar) and those reported by Hazen (1977a) (taken at 42 kbar).

Although

have been made by Hazen

data are limited,

(1977a) on the effects

the following of pressure

conclusions

on ferromagne-

sian olivines: (1) The [Si04] tetrahedra in forsterite and fayalite are essen-

-s

tially constant

in dimensions

with

pressure,

increasing

tetrahedra

'"oz

.. .. ..'" j!.

i.e.,

2.11

are very incompres-

sible.

2.10

(2) The M(l) and M(2) octahedra

Ci

0 I

forsterite

:II

and fayalite

z

significant

:II

increasing in Figure (3) Pressure effect PRESSURE

compressions pressure,

appears

confirm 326

to have little

on octahedral

accurate

with

as shown

26b for fo r s t er Lt.e.

in forsterite.

(Kbl

Figure 26b. Variation of mean M(l)-O and M(2)-O distances in forsterite with increasing pressure. (From Hazen, 1976).

of

undergo

distortions

However,

data are needed this conclusion

more to and to

make more detailed olivine

conclusions' on the effect of pressure

on the

structure.

The unit cell volume rationalized

compression

structurally

and empty octahedra. 3 of about 10 A occurs

of forsterite

by considering

and fayalite

the reduction

In the case of forsterite at 50 kbar pressure.

can be

in volume of filled

a total volume reduction

Hazen's

(1976) study showed

that the M(l) and M(2) octahedra undergo volume reductions of about 0.7 and 0.5 A3, respectively, at 50 kbar. There are four M(l) and four M(2) octahedra per unit cell. Thus, about 4.8 A3 of the unit cell compression of forsterite The remaining

can be accounted for by contraction of filled octahedra. 5.2 A3 of contraction can be accounted for by compression

of octahedral

and tetrahedral

explanation

of the unit cell expansion

been made by Hazen expansion

of forsterite

hexagonal

with the remaining

octahedral

closest-packed

Using polyhedral

in a variety

3

due to volume expan-

sites in the approximately

array of oxygens.

compression

data from high-pressure

such as those by Hazen on olivine,

polyhedra

of the 13 A

for by M(l) and M(2)

70 percent

and tetrahedral

A similar

with heating has

(1976) who found that about 30 percent

expansion,

sion of unoccupied

volumes

structure.

over the range -196 to 1000°C is accounted

octahedral

studies

voids in the olivine

of structure

(Hazen and Prewitt,

structural

the bulk modulus

types has been related

1977; Hazen and Finger,

1979).

of individual to polyhedral The bulk

modulus

(Kp) of [Si04] tetrahedra in olivines is on the order of 2.5 Mbar or greater whereas Kp for [Mg06] octahedra is 1.5 Mbar (Hazen and Finger,

1979).

was calculated polyhedron

A K p value of 1.8 Mbar for [Fe0 . 6] octahedra in fayalite using the inverse relationship between bulk modulus of a

and polyhedral

volume

(S ) (K = l/S: Hazen, v -IP v (0.56 Mbar ) from Hazen and

compressibility

1976) and the Sv value for [Fe06] octahedra Finger (1977). As pointed out by these authors, polyhedra

in silicate

structures

is greater

Prewitt

(1977) indicates.

The polyhedral

larger

than the macroscopic

bulk moduli

bulk moduli of forsterite

(1.24 Mbar:

polyhedra, makes an important

compression

of olivines.

327

of

for olivines

are

(1.35 Mbar:

Hazen,

Yagi et al., 1975), indicating

1976) and fayalite pression

of vacant

the compressibility

than the study by Hazen and

contribution

that comto the bulk

Hazen

(1977a)

as a function

combined his unit cell data for forsterite

of temperature

and pressure

tion of state for ferromagnesian

=

V

(290

+

+

0.17XFa

temperature

0.000006T2)[1

(in A3), ~a

where V is unit cell volume

the following

equa-

olivines:

+

0.006T

to construct

and fayalite

in °c, and P is pressure

- p/(135Q

is mole fraction

in kbar.

- 0.16T] fayalite,

T is

Using this equation,

Hazen

predicted

the unit cell vO,lume of Fo90FalO under P,T conditions predicted at a depth of 100 km (approximately 1000°C and 30 kbar). The value pre3 dicted (295 A ) is almost identical to that of a pure forsterite at 600°C and 1 atm pressure. more accurate Summary

This equation will probably

high-pressure

of P, T, X Effects

The structural different

cell parameters on the Olivine

studies

temperatures

of olivines

undergo

become

revision when

available.

Structure of different

have shown that increases

compositions

in octahedral

and at

cation size

over the range 0.69 A (radius of Ni2+) to 1.00 A (Ca2+) and in temperature over the range 20 to 1000°C have qualitatively

the same effects

olivine structure. There is some evidence that [Mg0 ] octahedra 6 vines expand more than Mn-, Fe-, Ni-, or Ca-containing octahedra given temperature relatively general.

interval

(see Table 6); however,

minor effect relative The parallelism

to octahedral

between

the effects

or composition. ficantly,

are essentially In contrast,

up to critical

cation size.

Increases

cause an increase angle variance

of temperature

in octahedral

become

available.

pressible.

cation size also

as defined

on the olivine

higher quality,

using the bond

The high-pressure

structure

cannot be fully

high-pressure

studies

of forsterite

structural

data

and fayalite

by Hazen

showed that [Si04] tetrahedra are essentially incomThis finding is consistent with the results of such studies

of other silicates.

(8Si-0)

or increasing

parameter.

until additional,

structures

expand signi-

temperature

and octahedral

distortions

and compo-

of [Si0 ] tetra4 in temperature

the M(l) and M(2) octahedra

in temperature

in

by changes

limits, with increasing

The effects' of pressure assessed

unaffected

in oliover a

this seems to be a

thermal expansion

sition is in part due to the fact that the dimensions hedra in olivines

on the

[Si04] tetrahedra have a mean linear compressibility of only 0.13 Mbar-l in silicate structures, including olivine 328

(Hazen and Finger,

1978).

Olivine

octahedra

-

are quite compressible,

-1

(SMg_O = 167 Mbar ) predicted to be less com-1 -1 pressible than [Fe06] (SFe-O = 181 Mbar ), [Mn06] (SMn-O = 194 Mbar ), l or [Ca06] values from Hazen and Prewitt, Ca-O = 243 Mbar- ) octahedra 1977). Present data are insufficient to make further general conclusions

with

[Mg06] octahedra

(8

concerning

(8

the pressure

The picture as a function tetrahedra with

from the available

of P, T, and X is one in which

are interconnected

the tetrahedra.

limits

effect.

that emerges

Because

by pliable

octahedra

cations

structural

relatively

of this polyhedral

to (1) the size of octahedral

M(l) and M(2) sites;

olivine

rigid

which

[Si04]

share edges

edge-sharing,

there are

that can substitute

(2) the thermal stability

data

of olivines

in the

before

they

melt or, in the case of Ca2Si04, undergo polymorphic transformations less dense phases; and (3) the pressure stability of olivines before undergo

polymorphic

other phases. dimensional

transformations

In other words,

mismatch

ever, beyond

between

certain

ature, and pressure,

critical

the olivine

we now have some notions, why the olivine

points

dimensional

to exist stably.

reasons,

melting

can tolerate

limited

and [M06] octahedra; howvalues of octahedral cation size, temper-

studies,

different

structure

the octahedron-tetrahedron

(Fig. 3) is limited

they

to denser phases or break down to

[Si04] tetrahedra

comes too great for the structure

map

to

mismatch

Because

though not any fundamental

structure

field on the A2B04 and why olivines of different and different

polymorphic

be-

of these physical

structure

field

compositions

transformation

have pres-

sures. Bonding

in Olivines

Our current understanding any silicate mineral, mineralogists mining

since Pauling's

the structure

gether by relatively

consider

conceptual

minerals

overlooked

classic

of complex

and other oxide minerals

very useful

of the bonding

forces in olivines,

is still rather primitive.

model,

1929 paper on the principles

deter-

of silicate

forces.

While

this is a

clearly did not intend for us to

only in an ionic context as is apparent

1948 paper on the electroneutrality

329

of

of cations and anions held to-

electrostatic

Pauling

or in'

generations

ionic crystals have thought

as assemblages

short-range

Several

principle

from his often (Pauling, 1948)

and his recent paper

(Pauling,

Si-O bond has roughly

50 percent

(see e.g.

think of bonds

fined by Pauling

bonds

(1929).

controversy,

"bond strengths"

The Si-O bond is assigned

are assigned

a strength

strength-bond

1973; Ferguson,

length relationships

tural predictions,

near 0.33 valence

units.

Among viewpoint

the first studies were

Huckel Molecular

and bond overlap

with the geometry The conclusion standards,

populations

can be rationalized

of these studies

for making

of the olivine

More recently, ticated molecular

in olivines

from a covalent

and Gibbs

(1972a,b) which pre-

(EHMO) calculations for isolated

Gibbs, Tossell,

Tossell,

theories

of the olivine

tetrahedron-octahedron

[Si0 ] tetrahedra 4 compositions.

of various

are rather crude by today's

using a purely

surrounding

of [Si0 ] tetra4 covalent model. considered

octahedral

and co-workers (including structure,

edge conformation 1977; McLarnan

(1976) was successful

(~103°) opposite

of valence

cations,

only as

structure.

orbital

Xa) to study details

bond

struc-

like olivine.

is that the calculations

without

less than

about the nature of bonding

in olivines

from these studies, which

[Si04] tetrahedra,

and Gibbs

on bond

such empirical

was that part of the bond length variations

One criticism

1976,1977;

Orbital

of those present

hedra in olivines

isolated

Although

in a structure

the papers by Louisnathan

sented Extended MO energies

1974).

are quite valuable

of bonding

This

than 1.0 (see e.g.

greater

they offer little insight

that hold atoms together

near 1.0

during the last decade such that

short Si-O bonds have strengths

Brown and Shannon,

as de-

such as Mg-O, Fe-O, and Ca-O

strengths

concept has been extended

which

1980), is to

the idea being that long Si-O bonds have strengths

1.0 whereas

a model

covalent

in terms of relative

bonds,

that the

character.

can be taken of the effect of bond length variation

strength,

forces

his opinion

et al.«, 1980 versus Pauling,

cation-oxygen

in olivine,

bond strength account

Stewart

in minerals

and other "weaker"

covalent

the ionic versus

One way of avoiding still arises

1980) reiterating

have used more sophis-

SCF-NEMO,

particularly

in olivine

et al., 1979).

in predicting

the edge shared between

CNDO/2,

and SCF-

the shared

(Toss ell and Gibbs, The study by Tossell

the correct O-Si-O angle

tetrahedron

and octahedron

using

an SiMg08HlO molecule as a model. They concluded that an important contribution to the minimization of total energy of this molecule at the above angle is covalent

overlap

repulsion 330

between

Si and Mg across

the

shared

edge.

The CNDO/2

three

which

consisted

in a minimum

the Tossell-Gibbs

the determinants

shared

energy geometry

study.

sive forces between

Instead,

However,

similar

in causing

the minimum

forces and that repulsive

favor long shared edges.

These workers

shared-edge

tetrahedra

distortions

bonding

and co-workers

and, therefore,

The important

point to remember

to the best bonding

calculation

The interesting

model

observed

Td

calculated

that silicon

for the present.

third rule, according

and theoretically

1971) and x-ray photoand quartz.

valence MO energies

for an isolated

is shown in Table 9.

was used as a model for olivine. XES and XPS spectra metal

in modeling

orbital

The com-

The quan-

and observed MO energies

cations.

is not

energies

equilibrium

331

greatly

as shown by the cal-

geometries

and the method

This re-

are not affected

However,

et al. (1979), second nearest-neighbor

of McLarnan

in oli-

good in light of the fact that an isolated

molecule

by second nearest-neighbor

et al. (1979)

distortions

of olivine

point symmetry

between

but is remarkably

are very significant

(Kuroda and Iguchi,

and predicted

with

of McLarnan

(1977) compared

(Nefedov et al., 1972) spectra

Using observed

of Baur

to date.

study by Tossell

the x-ray emission

culations

for

than those of Baur and Vincent

using Pauling's

electron

sult suggests

that dimen-

As pointed out

is that shared-edge

analyzed

[Si04] tetrahedral

on a com-

to the suggestions

should carry more weight

vine cannot be simply interpreted

perfect

in~eractions

based

is not responsible

structures.

The conclusions

on a more rigorous

[Si04] tetrahedron titative agreement

covalent

(DLS) calculations,

is in contradiction

of DLS calculations.

between

of short-range

et al. (1976) who based their opinion solely on the

(1972) and Vincent results

of the molecule.

Si-Mg and Mg-Mg

and octahedra

in olivine-type

this conclusion

are based

in

that repul-

geometry with shortened

also concluded,

of MO and distance-least-squares

sional misfit between

earlier,

obtained

indicates

energy geometry

found that the equilibrium

edges is the result of a complex misture

and electrostatic

parison

to the results

this calculation

Si and Mg, and Mg and Mg across shared edges are not

these workers

bination

in olivine

of an [Si04] tetrahedron sharing edges with This "better" model of the olivine structure

[Mg06] octahedra.

resulted

distortions

7et al. (1979) made use of a cluster of Si03(OH)Mg3(OH)10 com-

by McLarnan position,

MO study of shared-edge

interactions

using MO methods.

of Kowalczyk

et al. (1974),

Table 9.

Comparison of olivine

of experimental (after Tossell, molecular

4a

l

and calculated 1977).

orbital

energies

3t

Sal

4t2

2

XES and XPS values for olivine

-20.2

-

-6.4

-3.0

Calculated

-17.2

-14.4

-7.3

-3.1

values*

* Calculated

Tossell

using SCF-Xa-Scattered

concluded

that the Si~O bond in olivine

(63% ionic character) concluded olivine

Wave method.

than in quartz

MO energies

(in eV) le,5t2

ltl

-1.1

0

··1.2 d(Si-O)

is weaker

Tossell

to Si02 + MgO, witp Mg-O bonds in olivine (periclase).

One final result of these MO calculation~ predicted

charge distribution

(+0.86), M(l)

(+l.38), M(2)

0(3) ("",0.81)calculated smaller

in olivine.

than the nominal

for oxygen)

in agreement

ciple which

states

centers because

(+1.31),0(1)

by McLarnan

stronger

worth mentioning

The CNDO/2 (-0.74),0(2)

(-0.82), and

et al , (1979) are considerably

with Pauling's

(1948) electroneutrality

distribute

themselves

ionic-covalent

character

The partial

tribution flected

covalent

character

of charge indicated

by the CNDO/2

in ex~erimentally-determined

(total electron (G. Lager, pers. Although

of bonds

of cation-oxygen

density minus densities

in olivine

calculations

electron

density

of spherical

prin-

among atomic

bonds such that the charge on an anion or cation is usually ±1.0.

is the

(+4 for Si, +2 for Mg and -2

of the partial

than

charges for Si

formal charges

that electrons

also

role in stabilizing

relative

those in MgO

1.634 A.

and more ionic

(58% ionic character).

that Mg-O bonds in olivine play a significant

0

=

less than

and the disabove are re-

difference

maps

atoms) of forsterite

comm., 1978).

MO calculations

of "olivine-like"

molecules

including

[Fe06] octahedra have not yet been carried out, at least one rigorous calculation has been made for an isolated [Fe06] octahedron using the SCF-Xa-scattered wave MO method by Tossell (1976). The results of this study can serve as an approximate olivines

for the present.

Tossell

model for Fe-O bonding

found that as Fe-O distances

duced, as they are with increasing and the e

g

crystal

in Fe-bearing are re-

pressure, the separation between the t 2+ 2g field levels of Fe increase as predicted by the

332

R-5 law of crystal-field bonds

and the width

[Fe06] cluster This result concerning

In addition,

is consistent

has minimal trast with

electron

Fe-O distance

with the predictions

the effect of pressure Mossbauer

ducing Mg-O distances

the covalency

of the valence

increase with decreasing

on high pressure

of Huggins (1975, 1976) of Fe2+-0 bonds based

studies.

It is interesting [Mg06] cluster

effect on the elec~ronic

structure

a great deal has been written

for first-row

transition

metal

of olivines

1968; Burns, 1970a, 1974, 1976; Runciman

(Farrell and Newnham,

1974; Walsh et al., 1976, among others).

intra-

model

of the interaction

its predictions of transition

level splitting pressures,

predicted

U

=

e is the electronic p is a repulsive

with point charge

ful applications

model,

relative

stabilities

and Ahrens? (Born-Haber)

1970);

details

especially

of Tossell

derived

as positive

energy model.

or negative

point charges,

is the Madelung

cation-anion

include

of Mg-, Fe-, and N'i-olivines and spinels

energies

for forsterite

stabilities

333

of the

(Gaffney

and experimental

(Raymond, 1971);

of the olivine,

Success-

of the equi-

(2) prediction

of the theoretical

and

K, of the

volume).

(1) predictio~

(Born, 1964);

using

constant,

separation,

from the compressibility,

olivines

(3) comparison

structure

at high

(1976).

of each, and the energy is calculated

in forsterite

of the relqtive

of energ~

or Madelung)

+ 2]; where V is the molecular

involving

the

as has been demonstrated

model which has been applied

charge, R is the minimum

M(2) position

absorption

(or structure

valence

= R/[9VR/~e2K)

optical

and for rationalizing

(_~e2 IR) (1- p/R), where ~

parameter

librium

diction

this is a purely elec-

In spite of this success,

all atoms are treated

the full nomin~l

the relationship

1966;

electrostatic

is the "lattice"

In this model,

(p

olivines

by the crystal-field

A second type qf purely

phase

Though

oc-

et al., 1973, 1974; Wood,

ca~ion partitioning,

cited above.

of

1965; White and Keester,

of d-electrons

metal-bea~ing

models

about the crystal-

are not borne out by the SCF-Xa results

to olivines

orbital

are useful for interpreting

and inter-crystalline

in the literature

using

in con-

cations in the distorted

tahedra

spectra

to note that re-

from 2.12 to 1.92 A

of this cluster,

for [Fe06] clusters. to the bond strength and molecular

Reinen,

trostatic

from 2.17 to 1.95 A.

on the covalency

in an isolated

in olivines,

field model

ligands,

of Fe-O

region of the

the finding

In addition bonding

theory.

(in energy)

spinel,

(4) pre-

and S-spinel

of COZSi04 (Tokonami et al., 1972); (5) calculation of the thermal vibration ellipsoids at the M(l) and M(Z) sites in Mg-olivine

polymorphs

(Ohashi and Finger, tallization

1973);

of silicates

rationalization

(6) rationalization

from silicate

1978).

ionic model

for olivines

energy model,

tances, which

the bonding

ionic or covalent

of olivines

As pointed

in olivines

The most rigorous cluster modeled

bonding

after

et al., 1979) indicates

geometry

that this geometry

of forsterite

and electrostatic

covalent

field theory and the structure

useful

for crystal-chemical

predictions

the predictive

success

model should not be interpreted of bonding

in olivines

and in other minerals

tions using the most rigorous atoms large enough McLarnan

et al. (1979) approaches

they employed calculation presently

Pauling

with

extended

not economically

basis

models

the basic

fully disordered

arrays

Some years

bond strength

description

must await further

detailed

available

structure.

this description.

set on a cluster

an accurate of bonding calcula-

and clusters

of

The study by However,

the method

a full ab initio

of the size required

is

feasible. CATION PARTITIONING

In the early 1900's metallurgists as Cu and Au in alloys

ionic

of stability

that it embodies

(CNDO/2) is not the most rigorous because

INTRACRYSTALLINE

phenomenon.

Though

,energy model are

or rationalizations

An accurate

bonding

to represent

forces.

of the modified

in olivines.

(McLarnan

they should not be taken literally.

as implying

description

atomic

is caused by a complex mix-

like crystal

and cation partitioning,

dis-

ionic descriptions

ture of short-range

Similarly,

interatomic

over the past few decades.

models

differences

of the

forces in a crystal.

to date on a sizeable

the equilibrium

and

features

should not be thought of in

and useful,

calculation

charge or

out by Phillips

terms even though mostly

have been popular,

of these calcula-

self-compensating

of all bonding

structures

that a point

such as the use of observed

are the result

In summary, purely

is valid.

(1965), there are several

structure

success

as indicating

of crys-

1976); and (7)

in olivine-type

The apparent

tions should not be interpreted

Williams

(Ohashi,

of the cation distributions

(Alberti and Vezzalini,

of the sequence

melts

can be arranged

first recognized in ordered,

and that such ordering later, mineralogists 334

IN OLIVINES that atoms such

partially

ordered,

and

is a temperature-dependent

suggested

that cations,

such

as Si and AI, may occupy two or more geometrically lographically fashion

nonequivalent

(e.g., Barth (1934) * suggested

spars could be ordered Ghose olivine occupy

(1962) first recognized

confirmed

of various

neutron

Ghose's

cations

workers

olivine.

in the silicate

Studies. olivines

1970; other references

and Hafner,

paramagnetic

et al., 1968; Michoulier

(Shcherbakova

has been invesincluding

listed in Table 5);

et al., 1966); Mossbauer 1973; Shinno,

resonance

et al., 1969; Weeks et al., 1974;

1974; Niebuhr,

tion spectroscopy

(Reinen, 1968; Grum-Grzhimailo

1970a,b;

et al., 1973; Wood, 1974); and vibrational

Runciman

are summarized

olivines

~,

1977); electronic

absorp-

et al., 1969; Burns,

The results predicted

27 shows the variation

spectroscopy

of these studies on the basis of of distribution

ionic radius for transition

metal-Mg

and orthopyroxenes.

Examination

Octahedral

of Table

the ordering by factors

of cations

in addition

additional

cations

is the crystal

gain by occupying

(1934)

in Olivines.

in the M(l) and M(2) sites of olivine to cation and site size differences.

factor for olivines

containing

field stabilization

the smaller

For example, T.F.W.

Cation Distributions

10 (see also Table 5) and Figure 27 suggests

obvious

*Barth,

Figure

with effective

Factors Affecting

sites.

1973).

and are compared with ordering

cation size in Table 10. coefficient,

1975; Rager,

1964; Huggins,

1974;

spectroscopy

Ziera and Hafner,

(Duke and Stephens,

x-ray

et al., 1969; Bush et al.,

1972; Duncan and Johnston,

Shinno et al., 1974); electron

The ordering

of techniques

(Bancroft et al., 1967; Malysheva

1970; Virgo

to

the first modern

over the M(l) and M(2) sites.

(Caron et al., 1965; Newnham

diffraction

spectroscopy

and appeared

However,

(Hanke, 1965; Birle et al., 1968)

using a variety

(see e.g. Finger,

(1965) later work on

in orthopyroxenes

concerning

to be disordered

octahedral

diffraction

site.

from X-ray and Spectroscopic

tigated by numerous

in feld-

the possibility of Mg-Fe ordering in 2 + cation would preferentially

of Mg-Fe olivines

these cations

Observations

that the Al-Si distribution

Mg-Fe ordering

his prediction

x-ray refinements

or disordered

that the larger Fe

the larger M(2) octahedral

strengthen

in an ordered

or disordered).

and predicted

hypersthene

showed

sites in a mineral

similar, but crystal-

transition

is affected The most metal

(CFSE) these cations

and more distorted

in Mg-Co olivine,

Polymorphic

energy

that

phenomena

of the two octahedral the larger Co2+ cation is ordered

and crystal

335

structure.

Am. J. Sci., 227, 273-286.

Table 10. Comparison of predicted and observed octahedral ordering in the olivines and pyroxenes. Olivines*** M(l) M(2)

Predicted** !:J.r(A)* M(l) M(2)

M-Cations

cation

Pyroxenes*** M(l) M(2)

Mg - Ni

0.03

Ni

Mg

Ni

Mg

Ni

Mg

Mg - Co

0.025

Mg

Co

Co

Mg

Mg

Co

Mg - Fe

0.06

Mg

Fe

Fe

Mg

Mg

Fe

Mg - Mn

0.11

Mg

Mn

Mg

Mn

Mg

Mn

Mg - Zn

0.02

Mg

Zn

Zn

Mg

Mg

Zn

Mg - Ca

0.28

Mg

Ca

Mg

Ca

Mg

Ca

Fe - Mn

0.05

Fe

Mn

Fe

Mn

Fe - Ca

0.22

Fe

Ca

Fe

Ca

Fe

Ca

Ca

0.17

Mn

Ca

Mn

Ca

Mn -

*Calculated using Shannon's (1976) effective ionic radii. **Predicted solely on the basis of difference in cation and site size. ***Observations from x-ray site refinements. Pyroxene distributions from Ghose et al. (1974). Distribution for Mg-Zn olivine from Ghose (pers. comm., 1975).

100r--------------------------------, OLIVINE ORTHOPYROXENE

10 5

.. c

!

q

5

0

c

0

"

a~.,

'I

Mn

01L 0-6

Figure 27. Log KI) VB cation radius for 011vinas and orthopyroxenes containing Mg and the tranaition "",tab MD, Fe, Co, Ni, and Zn. Data are froll the following source.: Ni-Mg olivine (llajamani lit 1975); Co-Mgolivine (Gho•• lit aL, 1974); Fe-Mg olivine (Brown and' Prewitt, 1973); Fe-MDolivine (Brown, 1970); Ni-Mg, Co-Mg, Zn-Mg, Fe-Mg, and MD-Mgorthopyroxenes (Ghose et al., 1974). The vertical line through the point for Fe-Mg olivines express .. the range in KDvalues. (From Rajamani et aZ., 1975).

l-

Effective

..____.J

-'-

0-7

08 ionic

09

radii

336

preferentially

into the smaller M(l) site.

Similarly,

in Mg-Fe olivines,

2

the larger Fe + shows a slight preference for the M(l) site (see Table 5). 2 of the CFSE of Fe + in the M(l) and M(2) sites of a F0 using 88 optical absorption spectroscopy (Burns, 1970a) showed that the CFSE gained

Measurement

by Fe at M(l) is 12.9 kcallmole, mole.

Other estimates

the difference

in CFSE between

with Fe favoring tional optical

M(l)

that gained in M(2) is 13.1 kcal/.

at.,

as quoted in Ghose et

measurements

to resolve

suggest

that

M(l) and M(2) is on the order of 140 kcal

(Huggins,

absorption

vines are needed

whereas

of the CFSE gained by Fe in olivine

1976).

on well-characterized

this discrepancy.

Although

Addi-

Fe-Mg oli-

no CFSE measure-

ments have been made for Co in olivines, measurements have been made for 2 Ni + by Wood (1974) who found that Ni gains 27.3 kcal/gm atom in M(l) and 25.7 kcal/gm

atom in M(2).

Walsh et al. (1976) calculated

in CFSE for the M(l) and M(2) sites in Ni-bearing which

compares

reasonably

olivines

with the 1.6 kcal measured

a difference of 1.9 kcal,

by Wood.

These in-CFSE at M(l) and M(2) for Co2+ and

workers also estimated differences 2 Fe + to be about 1.0 and 0.8 kcal, respectively, indicating that crystal field effects cause strong ordering of Ni2+ in M(l) and less ordering of 2 2 Co + and Fe + in the M(l) site of olivine. Ghose et al. (1976) suggested bonding

predicted

that the greater

for the M(l) site of olivine

isomer shift values

is also a factor which

degree of covalent

on the basis of Mossbauer

favors cations

of relatively

high electronegativity

(Fe, Co, Ni, and Zn) in the M(l) site of olivines. This seems to be a reasonable explanation for Zn2+ which gains no CFSE in either M(l) or M(2) because of its dlO electronic configuration and

may be a factor in the observed

preferential

ordering

of Fe, Co, and Ni

in M(l). In light of the above data, the effect of certain factors

on the distribution

sites of olivines (1)

In the absence the smaller

(2)

of crystal

cations in the M(l) and M(2)

as follows:

. f~eld

cation is preferred

is consistent Mg-Ca,

of octahedral

may be summarized

crystal-chemical

with the ob~erved

(Mn

2+ ) or covalency

(Zn

2+ ) effects,

in the smaller M(l) site. distribution

This rule

of cations in Mg-Mn,

and Mn-Ca olivines.

The transition

metal cations

and more distorted

Fe2+, C02+, and Ni2+ prefer the smaller

M(l) site of olivine because 337

of the CFSE they

gain relative discussed

to M(2).

The measured,

above are consistent

or estimated,

with the observed

CFSE values

ordering

of these

cations in olivine. (3)

The more electronegative prefer

the M(l) site relative

greater

In addition

Nover

effect on ~

Shinno

in Fe-Mg olivines

Their interesting

equilibrated

by Shinno

findings

at different

such as

have been shown to have a (1974) and Will and

are summarized

below.

measurements

temperatures

on synthetic

in order to study the

dependence

of Mg-Fe distributions. He found that in a sample 2 at l150°C, Fe + is strongly partitioned into M(l) [~= 3.16];

equilibrated

equilibrations

at 950 and 800°C resulted

cients of 1.85 and 1.32, respectively, This result is surprising

in the orthopyroxenes.

indicating

equilibration

an increase expected

temperature,

Shinno found that redistribution

to temperatures

Will and Nover

in distribution

in light of the normally

cation disorder with increasing

continued

this site allows a

factors, variables

and oxygen fugacity

(1974) carried out 57Fe Mossbauer

temperature

further

to Mg because

to these crystal-chemical

temperature

(1979).

olivines

such as Zn2+,

metal cations,

degree of covalent bonding.

equilibration measurabl~

transition

coeffi-

in disorder.

increase

in

as is found of Fe and Mg

as low as 600°C in his experiments.

ordered volcanic olivines -16 -21 at 10 and 10 bars 88 p02 and measured the Fe-Mg site distributions using x-ray site-refinement techniques. Buffering at a p02 of 10-16 bar caused increased ordering 2 of Fe + in M(l) in both olivines (~ = 1.2), whereas buffering at a p02 21 of 10bar reduced ~ to 0.80 in both samples, indicating a reversal 2 in ordering with Fe + now showing slight preference for the M(2) site. (Kd

=

(1979) buffered

slightly

1.06 - 1.09) of compositions

These experimental equilibrated

at high temperatures

at relatively greater

suggest

Olivines

or metamorphic

tively low oxygen

should have ~

equilibrated origin which

olivines origin)

values

at low temperatures have cooled slowly)

and

significantly (i.e." those and at rela-

fugacities

near 1.0, indicating Althpugh

that natural Mg-Fe

(i.e. those of volcanic

high oxygen fugacities

than l.O.

of plutonic

studies

F090 and F0

should have KD values slightly below or slight ordering of Fe2+ on M(2) or disorder.

there are some exceptions

in Table 5 for Fe-Mg olivines

to these generalizations

from various 338

parageneses,

found

metamorphic

olivines

tend to have low ~

have higher low oxygen

~

values.

fugacity

Thus, it appears

have relatively

volcanic

high ~

than oxygen

olivines

values centered

fugacity

of equilibration

temperature

of

at 1.13.

temperature

in determining

The effect of Fe-Mg content on ordering

the effects

tend to

which formed under conditions

that the effect of equilibration

rate) is more important tributions.

values whereas

Lunar olivines

(or c901ing Fe-Mg dis-

is less clear than

or oxygen fugacity.

However,

Shinno et al.,

(1974) and Ghose et al., (1976) have found that in olivines 2 with more than 20 mol % Fa, Fe + tends to prefer the M(l) site with this site preference

decreasing

They also generalized

with decreasing

equilibration temperature. olivines, Fe2+ prefers the M(l)

that in Mg-rich

site at high temperature

but may prefer

the M(2) site at low tempera-

ture.

are consistent

with the Fe-Mg distributions

These suggestions

from two lunar olivines are believed

of different

compositions

(Fa

33

to be from the same lunar rock (#120lS).

and Fa ) which lS Finger and Virgo

(1971) found that the Fa33 olivine had a ~ of 1.75, whereas (1973) found that the FalS sample had a ~ of 1.15.

Brown and

Prewitt

olivines,

which

different

distribution

in composition.

presumably

coefficients

those by Ghose et al.

(1976).

similar

oxygen

fugacity,

Buseck

(1973) and Misener

factors

pressure,

affecting

exchange lower.

between Although

directly dependence

study

1974).

temperature,

temperature

and

in olivines

increases

and p02' but decreases

The minimum

in inter-

The studies by Buening

show that diffusion

at which Fe-Mg

sites takes place is at least 600. C and is probably the results

applicable

of the above diffusion

to exchange

between

of Mg and Fe diffusion

it now appears

are not

sites, they do show a dir~ct

on the variables

listed.

found in early studies

that Fe-Mg distributions

339

studies

as

as a func-

as a function

o

In spite of the lack of Fe-Mg ordering olivines,

as are

of Fe and Mg

of equilibration

and composition.

Fe content,

(Misener,

the exchange

is the difference

(1974) of Fe-Mg interdiffusion

of these variables

of pressure

conclusion,

There is a clear need for further

of these cations as a function

tion of temperature,

of their difference

as a tentative

the M(l) and M(2) sites of olivines

a function

show

in olivines.

Among other possible

diffusion

cooling histories,

perhaps because

This must be viewed

of Fe-Mg distributions

between

experienced

These lunar

are variable

as a

of

function

of equilibration

(possibly)

pressure.

distribution thermal

However,

oxygen

it is unlikely

fugacity,

or oxygen fugacities

Before we compare orthopyroxenes, in silicate

olivine

of composition

LiScSi04

the M(l) site and.Sc3+

is consistent

lithiophilite

merits

occupies

with the ordering

[LiMnP04]

(Geller and Durand,

in olivines

some mention.

and

The

(1976) showed that

the M(2) site

of monovalent

in the M(l) sites and of cations of higher

of

them.

study of cation ordering

study of this phase by Steele et al.

x-ray structure Li+ occupies

cation ordering

of one additional

and

used as an indicator

of the rocks containing

intracrystalline

the results

composition,

that the intracrystalline

of these cations will become widely

histories

finding

temperature,

This

cations

(Li and Na)

charge in the M(2) sites of 1960); triphylite

[Li(Fe,Mn)

P04] (Finger and Rapp, 1969); and natrophilite [NaMnP04] (Moore, 1972), which are olivine isostructures. Although Alberti and Vezzalini (1978) attempted

to rationalize

their results observed

this ordering

cannot be considered

structures,

with ordered

using Madelung

very meaningful

cation distributions,

their calculations.

Thus the calculations

ordering

At the present

predicted.

for the preference On the basis Weeks et al.

of monovalent

energy calculations,

because

cations

as the basis

had a built-in

time, no adequate

they utilized for

bias for the

explanation

for M(l) in certain

exists

olivines.

of EPR experiments

(1974) suggested

on Fe3+-doped synthetic Mg2Si04, 3 that what little Fe + exists in natural

forsterites

should occur in the M(2) site. On the other hand, the EPR 3 study by Ziera and Hafner (1974) found Fe + disordered over the M(l) and M(2) sites. Because Fe3+ has a d5 electronic configuration, it gains no CFSE.

Therefore,

crystal-field effects have nothing to with the site 3 distribution of Fe + in this case. Consideration of size differences between Mg2+ (0.72 A) and high-spin Fe3+ (0.645 A) leads to the prediction that Fe3+ should occur in the smaller M(l) site. However, this prediction

is not consistent

yet unknown

factors

with observation.

Perhaps

the same as

that result in Sc3+ ordering

into the M(2) site of here, too. Cr3+, which

(Steele et aZ., 1976) are operative 4 can gain CFSE in distorted octahedral sites, was found to order more

LiScSi0

strongly

into M(l) than M(2)

(Rager, 1977).

Corrrparisonof Intracrystalline Orthopyroxenes.

Cation Partitioning

As shown in Table 10 and in Figure 340

in Olivines and

27, there are some

OLIVINE

O(lA) 0(2)

0

0

0(1)

0(3)

2+ Hg (0.72)

........,_.).

2 Mn +(O.83)

--'-+

a(2A) (18)

Hl

0(18)

/

\

0(28)

0(3) c a(1A) (

~ 0.(1)

2

+ (0. 78)

-.--

Fe

J_

Ni2+(0.69)

I "'-1co2+(O.745) 0(2)

2+ ........,.-

Fo

I

H(l)

M(2)

2.101

2.135

Zn

(0.74)

En

A

I

H(l)

H(2)

I

2.070

2.158

0.086

211.8

182.6

A

0

Bond Ang. Variance

0.034A

Bond Ang. 114.6

107.8

0.0

0.0

6.8

Variance Avg. Charge Balance

Avg. Charge Balance CFSE

28.

crystalline from

0.2

13.1

12.9 Figure

0.0

Burns

CFSE

kcal

Comparisonof some of the factors cation partitioning in forsterite

I

29.2

-0.66 11.5

0.0

-0.66

11.7

0.2

kcal

affel!t inter- and intraand enstatite. CFSE values that

(1970).

striking

differences

in the observed

olivines

and orthopyroxenes.

ordering of octahedral

cations in

Although Ni-Mg and Mg-Mn olivines and

orthopyroxenes

show qualitatively

similar ordering,

Zn-Mg olivines

and orthopyroxenes

exhibit opposite ordering schemes.

In order to aid in understanding teristics

these differences,

some of the charac-

of the M(l) and M(2) sites of olivine and orthopyroxene

compared in Figure 28. and Rajamani

The discussion

are

below follows that of Brown (1970)

et al. (1975).

In spite of the large differences orthopyroxene

relative

in the M(l) and M(2) sites in

to olivine, Ni is only slightly enriched in the

M(l) site of orthopyroxene. ordering

Co-Mg, Fe-Mg, and

In addition,

Fe, Co, and Zn exhibit strong

into the M(2) site of orthopyroxenes

in contrast to the pref-

erence of these cations for the M(l) site in olivines. In the case of 2 Ni +, if cation size, site size, or crystal-field stabilization alone, or in combination,weremainly

responsible

then Ni should exhibit stronger ordering the olivine structure. the ordering.

Another

factor,

A key difference between 341

for cation site preference, in the orthopyroxene

than in

or factors, must be preventing the olivine and orthopyroxene

structures,

which

is related

to the above observations,

is the valence

balance at the oxygens. In olivine, each oxygen is surrounded by one 4 Si + and three M2+ cations, leading to formal valence balance in the Pauling

sense.

However,

in orthopyroxene

(-1/3) and 0(3A) and 0(3B) are overbonded

are underbonded

O(lA) and O(lB) are charge balanced M(2) site has as many overbonded therefore,

charge balanced

two underbonded

oxygens

(X =

(see Fig. 28).

on the average.

Considering

[M(l)] with

transition

ference

ca~.

to prefer

oxygens because

Aside

then from differences

in the sizes

of these sites leads to the relative

Using different

reasoning

than that presented

the dif-

enrichments

above, Ghose

et al. (1971) and O'Nions and Smith (1973) also concluded

(1962), Burnham

that the M(2) site of pyroxene INTERCRYSTALLINE Olivine

of underbonded

to a

of Mg

of the M(l) and M(2) sites in orthopyroxenes,

in "ionicity"

observed.

leading

more easily to them than the more electronegative

metal cations

and distortions

and is,

the M(l) site has

oxygens,

1.8), Mg is predicted

the higher proportion

it can lose electrons

However,

oxygens

the electronegativities

eX ~

1.3) versus Fe, Co, Ni, and Zn

(+1/3), whereas

'The orthopyroxene

as it has underbonded

and four charge balanced

of -2/3.

net underbonding

the site

the 0(2A) and 0(2B) oxygens

is more "covalent"

CATION PARTITIONING

BETWEEN

than the M(l) site.

OLIVINE AND OTHER SOLID PHASES

- Orthopyroxene

Considerable

interest

between

coexisting

classic

study by Ramberg

solid phases

of Mg and Fe between different

origins.

partitioned preference

in natural

(intercrystalline

and DeVore

coexisting

(1951) which

olivines

into orthopyroxene

+ ~;)/2 > 0.65].

studies

of Mg-Fe

assemblages

More recently,

in rocks of

29, that Mg is strongly

for Fe-rich bulk compositions

[(~!

1969,for

and shows no

in the more Mg-rich

These observations

exchange between

(see Medaris,

olivines

1974; Sack, 1980).

1969; Grover and Orville, In addition,

and orthopyroxenes

references

to this work).

1969; Matsui

the temperature

change reaction 342

bulk

have been confirmed

these and other data have been thermodynamically

(see e.g., Saxena,

since the

the partitioning

and orthopyroxenes

for olivine

of cations

partitioning) examined

They found, as shown in Figure

to a slight preference

compositions by numerous

has been shown in the partitioning

dependence

analyzed

and Nishizawa, of the ex-

'.0

0.0

.,., .,

0.7

C

';;

0

o.e

Q) IJ_

+ CO

::::!E

'"'." ::::!E

ef X

x:.

= Mg/(Mg + Fe) Orthopyroxene

Figure 29. Distribution of Mg between coexisting olivine synthetic samples. (From Grover and OrVille. 1969).

has been investigated tunately,

Medaris

sensitive,

in an experimental

at least in his analysis,

this exchange barometry. dynamic

study by Medaris

found that this reaction

cause it is not pressure-sensitive has not yet proved

However,

relating

found that in assemblages

(Ramberg and Devore,

containing

and Banno

re-evaluated

and ordering

olivines

pairs besides

Mg-Fe

(1969) studied

in coexisting

lites and garnet peridotites titioned

into the olivine,

and that Mn is strongly vation was confirmed

Unfor-

or geo-

the thermo-

for this pair.

in the composition

range

of other element

and orthopyroxenes

from lherzo-

and found that Ni and Co are strongly that Zn shows a slight preference

partitioned

into orthopyroxene.

by the experimental 343

He

orthopyroxene-olivine

the partitioning

olivines

Be-

1951),

to be useful in geothermometry

exchange

and

temperature-

over the range 700 to l300°C.

either

FolOO to FoSO or F040 to FalOO' a newly calibrated geothermometer is potentially useful. Matsui

(1969).

is not appreciably

Sack (19S0) has recently

formulations

and orthopyroxene in natural

par-

for olivine,

This last obser-

study of Mg-Mn partitioning

between

olivine

applied

their data to the estimation

tions during

and orthopyroxene

the formation

These observations chemical

reasoning

crystalline

(see Fig. 28).

In the absence

relative

in discussions

in olivines

of crystal-field

and in orthopyroxenes

effects,

preferentially

the larger cation

bears

this prediction

into the M(l) site of orthopyroxene,

to the M(l) and M(2) sites of coexisting

discussed

of the intra-

which has the larger M(2) site of the pair.

2 of Mn + into orthopyroxene

site of orthopyroxene,

olivine

and the M(2)

of the higher "ionicity" of this site as 2 2 Ni + and Co + are strongly partitioned into the M(l)

earlier.

because

site and, to a lesser extent,

the M(2) site of olivine because

in CFSE they receive

to the orthopyroxene

relative

gains no CFSE in either phase and usually it partitions Olivine

into the phase where

In coexisting Fe + partitions

orthopyroxene

olivine-orthopyroxene

preferentially

of the gain Zn2+

Because

to form covalent

bonds,

bond most strongly.

pairs from natural

into the olivine

this exchange

pair

in Mg-rich

is similar

bulk compo-

(Obata et al., 1974).

bulk compositions

(the major difference

assemblages,

to that found in the olivine-

between

orthopyroxene

is that the M(2) site in the latter is considerably

torted than in the former). experimentally,

geothermometer

Powell

and Powell

and attempted

clinopyroxene

temperature

of the expression

more dis-

has not been studied

olivine

had been established

However,

is likely to be unreliable

Wood

by Obata

analyzed

using groundmass

temperatures

range over which

and clino~

as a geothermometer

(1974) thermodynamically

oxide geothermometer.

that this geothermometer of the limited

this exchange

a calibration

in lavas for which

the iron-titanium

Perhaps

Although

it has been used empirically

et al. (1974).

stricted

prefers

it can covalently

No data exist for Fe~rich

Not surprisingly,

pyroxene

sites.

- Clinopyroxene

2

sitions.

condi-

using the same crystal

earlier

of these cations

in orthopyroxene,

Mg2+ partitions

(1972), who

and temperature

of peridotites.

can be rationalized

The strong partitioning out.

and Matsui

of pressure

that was employed

distribution

is preferred

by Nishizawa

this and using

(1976) concluded

as formulated

it was calibrated

because

and the form

for temperature.

a more reliable

geothermometer,

in use, is the one involving

344

though one that is more re-

partitioning

of Ni between

coexisting

olivine brated

and clinopyroxene.

Hakli and Wright

this geothermometer

augite,

and groundmass

Makaopuhi

by measuring

the Ni partitioning

glass using samples

lava lake in Hawaii

(1967) formulated

collected

and cali-

among olivine,

from the modern

and for which equilibration

temperatures

had been measured. Using this active, natural laboratory, they found 2 that Ni + is strongly partitioned into the olivine relative to glass and augite and less strongly

partitioned

also found that this partitioning thermometer

was later applied

the prehistoric

Makaopuhi

One geobarometer and orthopyroxene Ca solubility been studied (197S).

into augite relative

is temperature

lava lake in Hawaii olivine

in forsterite

coexisting

against

pressure

temperature.

estimates

This finding

sure confirms

In addition

to the above studies, of various

between

and spinels,

olivine

Olivine

chemistry.

However,

it can be considered

of partitioning

sults of these studies

with

pres-

from kimberencouraging

increasing

presearlier

this thermobarometer

reliable.

there have been recent measurements

elements between and between

are briefly

has

thermobarometer

and obtained

decreases

of

and Boyd

by Simkin and Smith (1970) discussed

element

needs further work before

and enstatite

xenoliths

geobarometer

that Ca solubility

on minor

dependence

is reduced with increasing

for garnet lherzolite

the suggestion

in the section

The pressure

They tested this olivine

lites made with the AI-orthopyroxene results.

with clinopyroxene

(1977) and Finnerty

They found that Ca solubility

sure and decreasing

This geo-

(Evans, 1969).

with diopside

by Finnerty

They

(Hakli, 1965) and to

coexisting

merits brief discussion.

experimentally

sensitive.

to a mafic intrusive

involving

to glass.

coexisting

olivines

summarized

olivine

and sulfides.

and garnet, The re-

below.

- Garnet of Mg and Fe2+ between

The partitioning been investigated

at high temperatures

olivines

and pressures

and garnets has by Kawasaki

and

Matsui (1977) and O'Neill and Wood (1979). The earlier study found that 2 Fe + is partitioned into garnets [(Mg,Fe2+)3A12Si30l2] relative to olivine at all Fe/Mg ratios and Wood confirmed the partitioning contents.

from 0.0 to 1.0. the findings

The more detailed

of Kawasaki

of Fe into garnet increases

These exchange

vine and the distorted

reactions

dodecahedral

and Matsui but also found that with increasing

are between

octahedral

(S-coordinated) 345

study by O'Neill

Mg and Ca sites in oli-

sites in garnets.

Optical pyrope

absorption garnets

spectral

by Burns (1970a) on almandinethat the CFSE of Fe2+ in garnet's dodecahedral

indicate

measurements

site varies values

from 12.4 (Alml) to 11.7 (Alm ) kcal/mole. Because these lOO 2 are lower than the CFSE of Fe + in either site in forsteritic oli-

vines,

the crystal-chemical

between

olivine

Finnerty and olivine volving

(1977) calculated

based on measured

for the observed

exchange

(Ca-Mg) and -3.76 and 0.49

garnets

between (Mn-Mg)

exchange between

between

olivine.

Fe-Mg partitioning

are not clear.

Ca-Mg and Mn-Mg

exchange

garnet and, separately,

for Ca-Mg and Mn~Mg

Olivine

reasons

and almandine-pyrope

other coexisting

The estimated

garnet

and olivine

garnet pairs in-

6Ho and 6So values are 19.00 andl.22

(all in kcal/gfw).

- Spinel

2 The exchange of Mg and Fe + between olivine and spinel of composi2 3 tion (Mg,Fe +) (AI Cr Fe +)04 has been investigated in a number of studies x y z before 1976 which are summarized by Fujii (1977). Fe2+ partitions preferentially into olivine at mole fractions of Cr3+ less than about 0.5 and of Cr3+ above 0.5 at temperatures above l200°C. At lower temperatures (550 to 700°C), Fe2+ is partitioned preferentially into spinel at all but the lowest mole fractions of Cr3+. into spinel

at mole fractions

Thus, as suggested and spinel

(1965), Mg-Fe2+

by Irvine

is a function

partitioning between 3 Cr + and temperature.

of mole fraction

The olivine-spinel geothermometer developed 2 ideal mixing of Fe + and Mg and gives reasonable studies

including

those of the chromitite

and of some ultramafic and Wright

intrusions

temperatures

of Hawaiian

tholeiitic

with Jackson's geothermometer 2 Fe +/Fe3+ ratios for spinels. between

(Loney et al., 1971).

coexisting

lavas.

However,

complex Evans

of the liquidus

of obtaining

A more recent experimental

olivine

in several

One of the major problems

is the difficulty

and spinel

ceases below about SOO°C. 2 The exchange of Mg and Fe + between

(1969) assumes

layers in the Stillwater

(1972) found that it gave a large overestimate

temperatures

exchange

by Jackson

olivine

accurate

study of Fe-Mg

(Engi, 1975) showed

that

exchange

and olivine

has been experimentally

kbar by Nishizawa preferentially

and Akimoto

coexisting

investigated

(1973).

at pressures

spinel

up to 90

They found that Fe2+ partitions

into the spinel polymorph.

346

(Mg,Fe)2Si04

Olivine

- Sulfide

Studies include

of Fe-Ni partitioning

between

those by Clark and Naldrett

olivines

(1972) and Binns and Groves

, strong 1y partltlone .. d' lnto F e 2+ lS

01" lVlne

sulfide

has a pronounced

phase.

This partitioning

dence and is, therefore,

and Fe-Ni sulfides

of potential

(1976).

an d N'12+ strong 1y pre f ers th e temperature

depen-

use as a geothermometer.

Summary The intercrystalline crystalline

phases

is temperature-dependent

above and, therefore, several

is of potential

geothermometers

them have marked (1976).

cation partitioning

These problems

their temperature models,

dependence,

atures before which proceed

Crystal-chemical possible using

components

(1976)*and

Detailed

lack of knowledge

experiments

exchange

represent

most of

Wood and Fraser

in the exchange

geothermometers

cations

to temperatures

Although

over the past decade,

by Wood

It should be emphasized

by these various

and other

cases, as discussed

reactions

and in part to the assumption,

of ideal cation mixing.

to sort out these effects. predicted

in certain

are due in part to a general

about the effect of other minor

olivine

use in geothermometry.

have been proposed

flaws, as discussed

between

on

in some

would be required that temperatures the minimum

temper-

ceases and that this exchange

can

of SOO°C and below. rationalization

of the cation exchange

for the olivine-orthopyroxene

the same arguments

ing in the last section.

behavior

and olivine-clinopyroxene

as we did for intracrystalline

is

pairs

cation partition-

consistent

simple crystal-field arguments based 2 CFSE for Fe + in olivines and garnets are not 2 with the observed enrichment of Fe + in garnets. The observed

enrichment

with the

greater

(Burns,

on Burn's

However,

(1970a) measured

of Ni in olivine-(Fe,Ni) sulfide pairs is consistent 2 CFSE gained by Ni + in sulfides due to TI-bond formation

1970a). MELT GROWTH OF OLIVINES The primary

purpose

cation partitioning review

available

AND OLIVINE

of this section

between

olivines

* Wood, B,J,

(1976) An olivine-clinopyroxene 297-303.

is to complete

and other phases.

data on the partitioning

melt and discuss how melt structure

- MELT CATION PARTITIONING

geothermometer.

Contrib.

of

We will briefly

of cations between

plays an important

347

the discussion

olivine

part in Mineral.

Petrol.,

56,

and

'.OOr------------:====----.

Figure 30. Polymer species distribution for melts in the system Mgo-Si02 calculated using the Monte Carlo method. The ordinat·e represents the fraction of oxygen atoms associated with the different polymer species. The abcissa is mole fraction MgO. The composition of forsterite falls at NMgo of 0.67. Si20-50 and Sb50 represen.t large polymeric units with between 20 and 50 Si and greater than 50 Si, respectively. (From Borgiani and Granati,

1979). 0.9

0.8

0.7

0.6

0.5

this partitioning. priate

melts

partitioning olivine

0.2

However,

to briefly

position

0.4 0.3

discuss

0.'

crystals

MaO

before we tackle this task, it seems appro-

the structure

in order to provide

of cations.

Jl

of olivine

and more complex

a bssis for understanding

We will also briefly

consider

from melts and the morphological

com-

melt-crystal

the growth of

variations

these crys-

tals display. The Nature

of Olivine

Composition

The most direct structural

Melts information

that is currently

available

of silicate

in the systems MgO-Si0

melts

x-ray studies the average,

comes from x-ray radial

composition

distribution

and FeO-Si0

2 In melts at or near olivine

1977, 1978).

on olivine

melts studies

(Waseda and Toguri,

2 compositions

in these systems~

have shown that Si occurs in isolated and that Mg and Fe are irregularly

mately

four oxygen

mental

studies,

ligands,

on the average.

In addition

recent Monte Carlo calculations

1979) were used to predict

the distributions

[Si0 ] tetrahedra, on 4 coordinated by approxito these experi-

(Borgiana and Granati,

of silicate

species

in MgO-

Si02 and FeO-Si02 melts. The calculation for the MgO-Si0 system pre2 dicted isolated [Si04] tetrahedra as the predominant species at the olivine composition

(see Fig. 30).

melts is not consistent composition

fugacities

the calculation melt structure

for FeO-Si0

2

for fayalite

melts.

The remarkable composition

However,

with the observed

melts (p02

=

x-ray studies by Waseda

and Toguri

(1978) of fayalite

at various temperatures (1250 to l400°C) and oxygen 7 11 10- to 10bars) showed that little structural change 348

occurs

in fayalite

conclude where

melt as a function

that a fayalite

fayalite

of these variables.

melt, just above the freezing

Thus we may

temperature

(1205°C)

crystals

first precipitate, consists primarily of isolated with Fe2+ cations in irregular tetrahedral sites, on the

[Si0 ] tetrahedra 4 average. The description l200°C

is similar.

tetrahedra easily

of MgO-Si02 melts containing 44 mol % Si02 at The lack of significant polymerization of [Si04]

is consistent

quenched

Melt Growth

,,,iththe observation

melt growth

(Jeanloz et al., 1977).

to glass

significant

gains have been made in our understanding

of crystals

from a macroscopic-thermodynamic

the last 20 years

(see review by Kirkpatrick,

an adequate

of melt growth

model

However,

in the case of olivine

it seems

safe to conclude

mate olivine

structural

model

45°C above

just above

or at the freezing melts,

among the first minerals ceeds and temperature tating minerals

including

crystal-chemical exercise

site as a basis phases

factors

responsible

structural Much

melts.

melt growth understanding

of olivine,

tetrahedral

polymerization

melt increases.

Mo:re recently,

Osborn

to octahedral

Although

lattice

(1954) rationalized using simple

(1976) went

through

a

energy per tetrahedral of various

do not directJ,y ad-

stability

phases

of different

and melt.

has come from experimental they have added little

349

pro-

about the crystal-chemical

in thermal

of the melt growth process.

are

in the precipi-

of appearance

these studies

in the crystallizing

although

olivines

of olivines,

Ohashi

the sequence

for differences

information

that Mg and Fe

and that as crystallization

tetrahedral

they give us some insights

arrangements useful

is based on the melt-

temperature.

using the electrostatic

growth,

melts,

from x-ray data taken only

from irregular

for rationalizing

from basaltic

dress melt

viewpoint.

composition

This work suggests

the early precipitation

principles.

over

of the melt may have an approxi-

which was derived

to crystallize

and remaining

these changes,

from olivine

it is well known that forsteritic

drops,

of

1975), we still do not have

This conclusion

temperature.

their coordination

In basaltic

growth

that portions

for fayalite

viewpoint

from an atomistic-structural

arrangement.

the greezing

must increase

similar

are not

of Olivines

Although

structure

that olivine melts

studies ,of the to our structural

The most notable

experimental

studies

of olivine

growth are those of Donaldson

his 1976 study, Donaldson crystal morphologies

experimentally

recognized

reproduced

cooling

liquidus,

rate and increasing

there are systematic

to skeletal. "skeletal

An important

olivines

1957).

changes in olivine

in picrites,

rocks

below the

morphology

reached by Donaldson

olivine-rich

basalts,

from granular is that the

and Archaean

fex' rocks are not due to rapid cooling but to rapid olivine by the high normative habits produced workers

olivine

by Donaldson

in natural

content

in a melt-structure nucleate

vine structure.

In complex

a certain

tetrahedra

by Flory-Huggins

tures.

Conceivably, similar

considered

context.

composition

fraction

Partitioning

crystal which distorted

knowledge

of cations between

of sites in the melt.

tions from studies As an example a cation' between olivine

and Whittaker formed olivines

to occupy isolated at high tempera-

compositions

melts and coexisting

the cations.

sites in olivine

fugacity,

into which However,

and melt,

(1967) analyzed from basaltic

crystals

between

There are two somewhat cations may partition we do not have much

of temperature,

pressure,

observa-

and melt pairs.

the partitioning

the partitioning

of

of Ni and Mg

melt.

the anomalous

Burns and Fyfe (1966) enrichment of Ni2+ in early-

rocks and concluded 350

olivine

might affect

consider

basaltic

is in-

sites in the melt and

because

as a function

of how melt struc~ure

olivine

and

These melt

we cannot fully rationalize

of cation partitioning

and a simplified

oli-

and Melt

of suitable

can stably accommodate

and oxygen

probably

for crystal growth.

Olivine

of cation sites in melts

composition,

between

Between

nu-

melts such as the ones studied by

theory, especially

to the availability

octahedral

from a variety

that olivines

of melt with an approximate

small melt volumes will attain

Element

related

by Fleet

of olivine

to the phase or phases on the liquidus.

could then serve as nuclei

The exchange

the mechanism

of Si atoms is predicted

polymer

volumes

timately

by other

rationalized

He speculated

as small volumes

Donaldson,

structures

Some of the growth

(1978a,b).

In a later study, Donaldson cleation

'spini-

growth caused

and observed

samples have been structurally

(1975) and 'T Hart

homogeneously

of the magma."

in his experiments

e.g.,

(see

He found that with in-

degree of" supercooling

conclusion

In

many of the olivine

in mafic and ultramafic

the classic paper by Drever and Johnston, creasing

(1975, 1976, 1979).

that solidus-liquidus

relations

in the binary

inverted.

Ni2Si04-Mg2Si04 crystalline to the Bernal liquid structure

According

1967) there are certain numbers

of tetrahedral,

than-octahedral-sites

in a given volume

was predicted because

predicted

of its high octahedral

dicted to preferentially

site preference

size.

With high concentrations

a typical basaltic

energy.

Ni

+

sites

Mg, on the other sites but is pre-

sites because

speculated

2

melt.

occupy octahedral

of large cations

melt, Whittaker

and larger-

of silicate

or tetrahedral

enter octahedral

series are

(see Whittaker,

octahedral,

by Burns and Fyfe to preferentially

hand, gains no CFSE in either octahedral

solution model

of its favorable

such as Ca, Na, and K in

that larger-than-octahedral

sites as well as some of the octahedral sites would be filled by these larger cations, forcing Ni2+ and Mg into tetrahedral sites. Thus, when olivine with two available Ni2+ would gain octahedral in the melts

However,

octahedral

sites

This series

in light of recent (see Whittaker,

how melt structure

1978).

may affect melt-

cation partitioning.

Measurements

of partitioning

melt have been made on natural Henderson

samples

Typical

olivine-glass

variations

cations between

31 and 32.

lished that exchange temperature,

high pressure dependence

experiments

with increasing

tallization

pressure

of depletion of olivine

1974; Takahashi,

1978).

of their octahedral

coefficient

olivine

fugacity,

are shown in

on

in those cases where vari-

concerning

of cations between

(Mysen and Kushiro, cations

estab-

and melt is dependent

Not enough data exist from

Ni partitioning

of metal

and McCarthy,

with temperature

experimentally

to draw conclusions

For example,

and

(see Irving, 1978, for a re-

are involved.

of the partitioning

in a few cases.

magnitude

and oxygen

state cations

1975; Cawthorne

data such as these have clearly

of cations between

composition,

able oxidation

pairs

determined

Experimental

olivine

(e.g., Hakli and Wright, 1967;

of distribution

for Ni2+ and Mn2+ ~artitioning Figures

of various

and Dale, 1969; Gunn, 1971; Mysen,

1977) and on synthetic view).

to grow,

from the tetrahedral

for liquid structure

does illustrate

and begins

sites in olivine.

should not be taken too literally

of the Bernal model this example

mineral

sites nucleates

CFSE by partitioning

to the available

of speculations criticisms

octahedral

the pressure

olivine

and melt except

into olivine 1979).

is reduced

In general,

the

in the melt caused by the crys-

is in the order Ni > Mg > Co > Fe > Mn (Roeder, Not surprisingly,

site preference

this sequence

energy, with 351

is in the order

the exception

of Mg.

015

o

o

o Leeman a Lindstrom ('78) o Hart et 01 ('76, in prep.) o Irvine Kushiro ('76) Mysen Kushiro ('76) + P. L. Roeder (unpubl.) Arndt ('77)

015

I:> Caley ('70)

Bird ('71)

a a

*

V Irvine ('75)

o Mysen ('780

c

Duke ('76)

5.0

"8

Figure 31. Variation of Znn for olivine reciprocal temperature frail>,a number of experimental studies of Ni partitioning. The distribution coefficient D is defined as follows: D • C(M)ol/C(M)liq where the C(M) terms are the concentrations of the metal cation, M, in olivine and liquid, respectively. (From Irving, 1978).

1200 OLIVINE I LIQUID

1100

IIIn

W.afson ('77) o Leeman ('74) + Roeder ( 74) x Bird ('71)

I>. Longhi et 01 ('78) o Lindstrom ('76) o Duke ('76)

o

+

o

o o 0

-F

a

,--o,~ ~ ~

~O~~~

o+~

o o

"8 reciprocal

Figure 32. Variation of Znn for olivines experimental studies of Mn-partitioning.

More recent perimental Kushiro, 1979),

studies

investigations 1979; Mysen,

(From Irving,

not discussed

(Takahashi,

(Takahashi,

include

1978; Mysen

1980), Ca partitioning

and Mg, Mn, Fe, and Co partitioning 352

from a number of

in the Irving review

of Ni partitioning

1979; Nahelek,

temperature 1978).

(Watson,

1978).

exand

of Ni2+ between

The partitioning extensively

studied

concerning between

whether

olivine

literature opinion, tioning

exchange

reaction

Ni behaves

and liquid.

and apparently

As pointed

to Henry's

coefficients

basalts

abundant

for transition

(100-300 ppm). (1977),

metal cations between

oli-

equilibrium.

SPINEL TRANSITION

-+-

composition

phase in the Earth's

formations

over the

(1978) and Leeman and Scheidegger

THE OLIVINE of approximate

The concensus

and liquids

vine and melt can be used to test for crystal-liquid

Olivine

(198D) review this

study, is that Ni parti-

in olivines

range found in most natural

the distribution

Law when partitioned

the controversy.

by Nabelek's

behavior

out by Takahashi

of the controversy

(1979) and Nabelek

have resolved

which has been confirmed

and melt has been the most

in part because

according Mysen

obeys dilute solution

Ni concentration

olivine

F0

is considered to be the most 90 upper mantle. The known polymorphic trans-

of Fo

to the S-spinel and y-spinel phases at pressures near 90 118 and 115 kbar, respectively, and atlOOO°C, result in density increases of approximately mations

7.7 and 10.2%, respectively.

are key elements

seismic wave velocities

in explaining

low pressure stabilities pressure

compounds

viewpoint

stability

of the olivine and y-spinel.

crystal

chemistry

spinel of composition named ringwoodite

(1975).

Ringwood

in

to spinel transformation rationalization

It is appropriate

(Mg.7,Fe.3)2Si04

review of the high

by.Akimoto

on high pressure

et al. (1976) is

transformations that a natural

from the Tenham meteorite

of A2B04 silicate has been so much

(Binns et al., 1969).

Phase Relations and Major

for the

type and the high pressure

The excellent

in honor of Prof. Ringwood who has contributed

in this area of research High Pressure

structure

of orthosilicates

as is the chapter

in Ringwood

the olivine

and offer a structural

of S-spinel

recommended,

these transforincrease

at a depth near 400 km.

In this section, we will examine from a structural

Therefore,

the discontinuous

in the System Mg2Si04-Fe2Si04

(1966) were

the first to publish

the high pressure

phase diagram discovered

for the Mg Si0 -FeSi04 system shown in Figure 33. They 2 4 a new, non-isotropic phase near the Mg-rich end of this diagram

and termed this phase S-spinel

after they suggested

353

that it had a "modified

spinel structure. 160

1000

-c

since been confirmed laboratories Structures ~2Si04

around

in several

has

other

the world.

of the S-Mg2Si04 Polymorphs

and

The structure

w 0:

~

This discovery

100

Si04, which

W 0: n,

of S-(Mg . Ni • ) O 9 O l is isostructural with S-

eo

(MgO.9FeO.l)2Si04'

was first deter-

mined by Moore and Smith

(1969, 1970)

60

using powder

data.

diffraction

found that the essential 40L__L __ 100

....,.0.

L_-L__L__L__~~

80

60

OLIVINE MO'JIFIED

101

SPINEL

20

0

mol·/.

J

SPINEL I

(I

features

of

__~~~

40

COMPOSITION,

They

I

rJ

I

Figure 33. Phase relationships in the system Ms2si04 - Fe2Si04 at pressures up to 140 kbar and at 1000·C. (From Akimoto et aL. 1976).

th.e structures

are the approximate

cubic closest packing

of oxygens

and

corner-shared [Si04] tetrahedra forming [Si207] sorosilicate groups. Mg and Ni occupy octahedral sites as in oli vine and each octahedron

o

shares six

0

Figure 34. Stereo-pair view of the structure of S-C02Si04 projected on (100). circles, oxygen; intermediate-sized circles. cobalt; smallest circles, silicon. Akimoto et al:.• 1976).

354

Largest (From

edges with other octahedra structure

but none with

has since been confirmed

for S-Co2Si04 Although

which

is pictured

tetrahedra.

and refined by Morimoto

in Figure

no crystals

by interpolation

et al. (1974)

34.

of y-Mg2Si04 suitable work have yet been synthesized, the u parameter estimated

The Moore-Smith

for single-crystal

x-ray

of this spinel has been

using the well refined

structures

(Yagi et al.,

for y-Ni2Si04 1974), and y-

1974; Ma, 1975), y-Co2Si04 (Morimoto et al., (Yagi et al., 1974; Finger et aZ., 1979). These values were re-

Fe2Si04 ported earlier

in the section

on "Olivine

and Spinel Structure

Type."

In addition, the u value of y-Mg2Si04 can be predicted using the regression model of Hill et al . (1979) and is found to be 0.3666. The structure of y-Ni2Si04 has been studied at pressures up to 38 kbar by Finger et al. (1979) who find the u parameter to be essentially constant with increasing pressure,

as is the Si-O distance.

Structural

Rationalization

Kamb

(1968) rationalized

vine and y-spinel edges in olivine

of (Mg,Fe)2Si04

are shortened

relative

are predicted

third rule.

He also noted

(both octahedron-octahedron

to y-spinel

because

of reduced

shared edge shortening Another

in stability by noting

to the unshared

to be lengthened

between

the oli-

that the shared edges, whereas in violation

and octahedron-tetrahedron)

repulsions.

counterbalances

of

edges in relative

edges) favors the y-spinel

cation-cation

in olivines

manifestation

of the a-, S-, and y-Polymorpl

that the types of shared

(only octahedron-octahedron

low pressures

effect.

the difference

polymorphs

those in y-(Mg,Fe)2Si04 Pauling's olivines

of the Stabilities

form at

However,

the

this destabilizing

of these observations

recognized

by Kamb

(1968) is found ~n the ratio of mean octahedral

bond length, dA, and mean dB' in A2B04 compounds of the olivine and y-spineJ types. Kamb found that those A2B04 compounds with dAldB < 1.9 preferred the y-spinel structure type whereas those with dAldB > 1.9 preferred the tetrahedral

olivine Fe2Si0

bond length,

structure

out by Mg2Si04 and which have ratios of 1.30 and 1.33, respectively. As pressure

4 is increased

This prediction

is borne

on olivine, we now know that the [(Mg,Fe)06]

press significantly Thus the distance which

type.

whereas

com-

the [Si04] tetrahedron remains constant. and eventually falls below 1.9 at

ratio is reduced

point the y-spinel

another way which

octahedra

polymorph

is formed.

follows our earlier 355

We can restate

discussion

this in

of the effect of pressure

on the olivine morph,

structure.

the octahedra

of shared edges between will eventually

reach

vine arrangement ments,

neither

As pressure

are compressed octahedra

increases

and tetrahedra,

a point with increasing

is unstable

on the olivine

but the tetrahedra

relative

structural

Because

the dimensional

pressure

to the y-spinel

rationalization

mismatch

such that the olior S-spinel

of which have shared octahedral-tetrahedral

A more elaborate

poly-

are not.

arrange-

edges.

of the stability

differ-

ences among the a-, S-, and y-polymorphs fered by Sung and Burns to those presented ferences

(1978).

above.

in structure

of M2Si0 compounds has been of4 However, its essential details are similar

Using quite a different

stability

of the polymorphs Therefore,

internal

in the order a > S > y. increase

the S-phase

based on dif-

energy among the a-, S-, and y-polymorphs,

et al. (1972) found that the calculated creasing

approach

energies

Tokonami

suggest

Their estimates

de-

of entropies

in the order y < S < a as do molar volumes.

is predicted

to have a field of stability

at high

temperatures. The effects transformation

of crystal-field

has been examined

stabilization

on the olivine ~ spinel

by Syono et al.

(1971), Mao and Bell

(1972), and most recently

by Burns and Sung (1978).

suggested

CFSE that certain

that the excess

in spinel relative pressures Fe2Si04

to olivine

to the y-spinel

and calculated

field effects.

(Mgl_xFex)2Si04

composition

They concluded

raised

polymorph

presumably

would

Navrotsky

lower transformation this effect in

study, Burns and Sung found that due

the olivine is ~owered

to y-spinel

transformation

in pressure

that this effect is equivalent

spinel boundary

cations gain

of about 98 kbar caused by crystal-

In a more detailed effects,

metal

Mao and Bell considered

a lowering

to crystal-field

lesser extent

leads to remarkably

phase.

Syono et al. first

transition

in

by about SOx kbar

to having

the olivine-

in the upper mantle by about 15 km.

The S-spinel

show this effect as well, but possibly

to a

than y-spinels.

et al. (1979) carried out high-temperature

calorimetric

measurements

on a- and y-Fe2Si04 and a-, S-, and y-Co2Si04 and from these data calculated the phase relations at high P and T. Their results agree qualitatively (1972).

with

the stability

relations

Their study shows that entropy

in determining

the relative

stabilities

356

proposed

effects

by Tokonami

et al.

are quite significant

of the three polymorphs

and are

not constant arguments

with

changing

composition.

This indicates

that structural

such as those made earlier may not be adequate

to rationalize

stability

differences among these polymorphs. They also found that small 2 4 of M +_Si + disorder in the y-spinel or S-spinel phase may have a

amounts

significant

effect

Geophysical

Consequences

Although

on phase boundaries.

detailed

these transformations marized (1)

briefly

of the Olivine discussion

is beyond

to y- and S-spinel

composition

is probably

The depth at which superadiabatic,

causing

they may be sum-

This transformation,

1972; Schubert

The transport

measured

in numerous

and, there-

pull on the slab (Ringwood,

1972;

for Fe-rich

compositions

and in the

deep focus earthquakes

(Ring-

et aZ., 1975; Sung and Burns, 1978).

of cations

(radiative

to the sur-

density

1976).

may trigger

TRANSPORT

and heat

slabs relative

in relative

the downward

especially

in

takes place is raised in the

lithospheric

of mineralizers,

for the (MgO.9FeO.l)2SiC

1969).

an increase

et al., 1975; Ringwood,

presence

of

for the 400 km discontinuity

(Ringwood,

this transformation

fore, acts to increase

wood,

transformation

responsible

descending

mantle,

Schubert

consequences

the scope of this review,

The olivine

rounding

(3)

of the geophysical

Transformation

as follows:

seismic wave velocities (2)

(y,ef-Spine1

+

transfer studies

PROPERTIES

OF OLIVINES

(diffusion), or lattice

charged

thermal

of olivines.

species

(conductivity),

conductivity)

A brief

summary

has been

of this litera-

ture is given below. Cation Diffusion Several

measurements

been made as functions crystallographic 1974),

(Co-Mg:

Morioka,

studies by Buening

increasing

diffusion

of composition,

orientation

(Fe-Mg:

1980),

(Ni-Mg:

(1) decreases

pressure,

of cations

temperature, Buening

and (3) increases

showed

357

1973; Misener, The

that interdiffusion Mg content,

with increasing

is sensitive

have

p02' pressure,"and

and Buseck,

with increasing

tion, they found that interdiffusion

in olivines

Clark and Long, 1971).

and Buseck and by Misener

Fe and Mg in olivine with

of lattice

of

(2) decrease

p02'

In addi-

to crystallographic

orientation direction

with the greatest of the octahedral

interdiffusion

chain in olivine.

in olivine was theoretically explained

the highest

analyzed

Misener's

The diffusion

by Ohashi and Finger

zig-zag

calculation

vines, based on his diffusion

to [001], the anisotropy (1974) who

rate along c by zig-zag jumps alternating

diffusion

along the M(1)-M(2)-M(1)-M(2)··· the M(l) chain.

parallel

chain rather than straight

of electrical

measurements,

conductivity

agrees with observed

through

in oliconduc-

tivity measurements. Morioka

measured

of temperature bility

and Buseck

relative

interdiffusion

to be temperature

to the c axis.

parallel

coefficients

The interdiffusion

and is greatest

intermediate.

for Fe-Mg

The order of these

can be rationalized

by noting

that the

energy of Ni2+, Co2+, and Fe2+ in oli-

site prefer~nce

in that order.

The diffusion

of Mg and Fe in olivines

et al. (1978) have proposed takes into account

a kinetic

diffusion

tion, as well as diffusion

model

can result in zoning.

Onorato

for zoning in olivines

which

in both solid and liquid during

crystalliza-

in the solid after crystallization

This model has been used to predict olivines

observed

and by Misener.

with Co-Mg interdiffusion

order of octahedral vines decreases

and found that Co-Mg mo-

to the Fe-Mg interdiffusion

is least for Ni-Mg in forsterite

interdiffusion,

for Co-Mg as a function

(1971) found Ni-Mg interdiffusion

and to be greatest

coefficient

orientation

is low compared

Clark and Long dependent

coefficients

and crystallographic

in olivines

by Buening

interdiffusion

and has been referred

zoning profiles

to by these authors

is complete.

and cooling

rates for

as an "olivine-cooling

speedometer." Conductivity There has been a great deal of interest of olivines dependence profiles period

of mantle because

composition

in the electrical

and its temperature-,

of the Earth.

The papers by Duba and co-workers

1973, 1974, 1976) are recommended literature

on olivines

conductivity.

pressure-

of the need for these data in constructing

1972 to 1976 (Duba, 1972; Duba and Nicholls, as an introduction

conductivity and p02-

geothermal

covering

the

1973; Duba et al., to the conductivity

and the effect of the above variables

on olivine

The papers by Will et al. (1979) and Cemic et al. (1980)

contain

a more up-to-date

present

new measurements

summary

of the past literature

on olivine,

including 358

Ni2Si0 , 4

on olivines as functions

and of

P, T, X, and p02'

The trends in conductivity too detailed

as functions

variables

are generally

to present

important

to point out that ferric iron and defects

otherwise

similar

can cause differences

here.

of these

However,

it is

in olivines

in conductivity

that are

of several orders

of magnitude. One of the most interesting the one carried

studies

out by Mao and Bell

They found that the absorption

of conductivity

in olivines was

(1972) at pressures

edges of the olivine

above 100 kbar.

and y-spinel

forms

of Fe2Si04 shifted rapidly with pressure from the near UV to the lower energy IR region with a simultaneous exponential increase in electrical conductivity. transfer

They attributed

this increase

Radiative

important

implications

is operative

radiation

would be severely

Radiative

heat transfer

experimentally

in olivines.

Lattice

Thermal

Thermal

conductivity

conductivity

accompany

A very extensive

effects

at low pressure

transfer by

than 500 km.

has been studied

et al:.. (1979) and discussed by Mao (1976).

(or thermal

to this type of transport

diffusivity)

properties

the olivine~pinel

AND MECHANICAL

literature

in olivines

Changes

transition

has been

in lattice

thermal

and the spinel4post-

PROPERTIES

OF OLIVINES

exists which discusses

of olivines.

for the derivation

under mantle

(1976).

in the mantle.

state and for an understanding

recommended

in the earth's manhe~

at depths greater

(1975) and by Kieffer

ELECTRICAL

is important

heat transfer in the mantle,

Conductivity

spinel phase changes

and elastic

by Mao and Bell (1972) has

serve as good introductions

process

studied by Holt

blocked

in olivines

by Shankland

These two papers

observed

about radiative

If this phenomenon

olivines

charge

Heat Transfer

The red shift of absorption

tle.

to a new, efficient

process.

An understanding

and utilization

of these properties

of olivine

of the flow properties

conditions.

the mechanical

equations-of-

and deformation

The recent paper by Jeanloz

as a source of information

in olivines. 359

and further

references

of

(1980) is on shock

Several synthetic

interesting

vine from the Coorara reported

peak pressures olivine

chondrite

the discovery

shocked-deformed

and unexpected

(Mason et al., 1968).

of glass of olivine

single

crystal of natural 9 of about 56 x 10 pascals.

glass; however,

may show that olivine of naturally

results were found in a shocked

(Jeanloz et al., 1977) and in a naturally

olivine

shocked

closer examination

composition peridot

olivine

Mg3Fe2Si30l2

an olivine

of composition

olivine.

et al.,

in an experimentally

(Fo

of naturally

from a chondrite

replacing

Jeanloz

) recovered from 88 This is the first report of shocked

olivine

The study by Mason et aZ.

glass exists in nature.

composition

shocked oli-

showed garnet of approximate These workers

suggested

that

F075 underwent transformation to garnet because The transformation 'of Mn Si0 (olivine) to MnSi0 2 4 3 plus MnO has been performed experimentally (Ringwood, 1975).

of some shock event. (garnet)

This transition

may be significant

The hardness studied mended

extensively

of olivine

in the earth's mantle.

and its temperature

by Evans and Goetze

elastic

properties

of the olivine,

and germanate

olivines

have been

(1979), and their paper is recom-

as a source of further references.

silicate

dependence

y-spinel,

Finally,

a discussion

and S-spinel

of the

polymorphs

can be found in the paper by Lieberman

(1975) .

360

of

TABLE Al.

OLIVINE FORMULAUNITS, SPECIl"IC

ABBREV.

FORMULAUNIT

(N1) (Fo)

(Hg.90Fe

(Co)

C025104

4.88 .10)2S104

(Ho)

(Mg.49

Fe.49

Mn.01

(Fa)

(Fe.92

"g.04

Mn.O.

Ca.002)2S104

(Zn-Pi)

(Mn.65"Mg.17

zn.ll

F•• 06 )2S104

3.96

Mg.02

)Z8104

4.16

(Kn)

(Fe.51

(Kg .50Ca .50) 25104

(Ki)

(Ca. 5 7 Fe. 43 ) 25104

(Gl)

(Ca.49

(

2.076(1)

2.101(1)

2.119(1)

2.128(1)

2.158(1)

2.148(1)

2.168(1)

2.135(1)

2.211(2)

[2] 0(1)_.o(3)b

2.813(4)

2.853(5)

2.882(3)

2.895(4)

2.93.0(3)

2.953(3)

2.961(2)

2.966(4)

3. .028(8) 3. .037(5) 3.2.0.0(9)

[2] 0(1)-0(3')

3.075(3)

3.122(4)

3.143(3)

3.156(4)

3.221(2)

3.178(4)

3.221(2)

3.132(4)

3.273(6)

3.277(5)

[2] 0(1)-0(2)b

2.845(5)

2.854(4)

2.884(4)

2.877(5)

2.9.02(3)

2.894(4)

2.932(3)

2.844(5)

2.952(9)

2.968(6)

3.121(12

[2] 0(1)-0(2')

2.990(1)

3 •.032(3) 3 ..038(1) 3•.064(3) 3. .098(2) 3.119(1)

3.114(1)

3.206(2)

3.259(2)

3.273(1)

3.449(3)

[2] 0(2)-.0(3')

3.289(4)

3.353(4)

3.396(4)

3.432(5)

3.510(3)

3.452(3)

3.514(2)

3.336(4)

3.569(7)

3.546(5)

3.942(8)

[2] 0(2)-0(3)8

2.556(4)

2.557(4)

2.57.0(3)

2.561(4)

2.576(2)

2.560(4)

2.582(2)

2.569(4)

2.587(5)

2.575(5)

2.61.0(8)

2.928(2)

2.962(2)

2.986(1)

2.998(2)

3 ..04.0(1) 3•.026(1) 3.054(1)

3. .0.09(2) 3.111(3)

3.113(2)

3.308(4)

2.2.05(4)

2.234(2)

M(2)

3.526(9)

OCTAHEDRON

[1] H(2)-0(1)

2.110(4)

2.17.(3)

2.187(4)

2.311(4)

2.286(2)

2.478(3)

2.452(4)

2.520(9)

[1] H(2)-0(2)

2.041(3)

2.057(3)

2•.071(3) 2•.081(4) 2.11.0(2)

2.144(3)

2.120(2)

2.3.09(4) 2.278(6)

2.3.08(4)

2.350(8)

[2] H(2)-0(3)

2.178(2)

2.221(3)

2.224(2)

2.3.05(2)

2.307(2)

2.411(3)

2.428(4)

2.414(3)

2.453(6)

[2] H(2)-0(3")

2.051(2)

2. .067(3) 2•.072(2) 2•.058(3) 2•.069(2) 2.139(2)

2.113(2)

2.289(2)

2.299(4)

2.3.03(3)

2.39.0(6)

1(2)-0>

2.272(3)

2.293(2)

2.463(6)

2.102(1)

2.135(1)

2.142(1)

2.208(1)

2.364(1)

2.366(2)

2.366(1)

2.426(3)

[2] 0(1)-0(3")

2.974(4)

3.027(4)

3 ..041(3) 3,061(4)

3•.084(2) 3.209(4)

3.16.0(2)

3.593(4)

3.555(6)

3.519(5)

3.542(9)

[2] 0(1)_.o(3)b

2.813(4)

2.854(4)

2.882(3)

2.895(4)

2.93.0(3) 2.953(3)

2.961(2)

2.966(4)

3.028(8)

3.037(5)

3.2.00(9)

[2] 0(2)-0(3)

3.155(4)

3.196(4)

3.220(3)

3.26.0(4)

3.304(2)

3.354(4)

3.341(3)

3.595(4)

3.597(6)

3.610(5)

3.703(9)

[2] 0(2)-0(3"')

2.886(3)

2.935(4)

2.927(3)

2.927(4)

2.954(2)

3.019(3)

2.979(2)

3.147(4)

3.118(6)

3.161(4)

3.261(8) 2.618(1.0)

2.158(1)

2.178(1)

2.224(1)

[1] 0(3)-0(3)-

2.6.07(4)

2.593(6)

2.593(5)

2.612(6)

2.608(3)

2.599(4)

2.596(3)

2.615(5)

2.571(8)

2.614(6)

[2] 0(3)-0(3")

2.974(3)

2.996(3)

3.006(3)

3.016(4)

3.022(2)

3.110(3)

3 • .oB2(2)

3.371(4)

3.345(5)

3.332(4)

3.331(7)

[1] 0(3")-0(3''')

3.3.04(4)

3.4.01(6)

3.4.08(5)

3.432(6)

3.491(4)

3.574(4)

3.550(3)

3.771(5)

3.898(8)

3.875(6)

4.166(1.0)

2.960(1)

3.001(1)

3.013(1)

3•.03.0(1) 3.057(1)

3.122(1)

3.099(1)

3.311(1)

3.313(2)

'3.317(1)

3.405(3)

[2] O(l)-M(l)o

2.065(2)

2.088(2)

2.098(2)

2.101(3)

2.123(1)

2.148(2)

2.146(2)

2.194(2)

2.224(5)

2.252(3)

2.343(6)

[1] 0(1)-M(2)o

2.110(4)

2.176(3)

2.187(4)

2.205(4)

2.234(2)

2.311(4)

2.286(2)

2.478(3)

2.463(6)

2.452(4)

2.520(9)

[1] 0(1)-81.

1.613(3)

1.620(4)

1.613(3)

1.625(4)

1.623(2)

1.610(3)

1.619(2)

1.615(4)

1.628(8)

1.620(4)

1.637(8)

1.963(1)

1.993(1)

1.999(1)

2.0.08(2)

2.026(1)

2.054(1)

2.049(1)

2.120(1)

2.135(3)

2.144(2)

2.211(4)

o(i)

TETRAHEDRON

[1] M(l)o-M(l)O

2.955(1)

2.997(2)

3.0.0.0(1) 3•.022(2) 3.050(3)

3.086(1)

3.073(1)

3.193(2)

3.234(2)

3.244(1)

3.392(2)

[2] M(1)S-H(2)S

3.138(1)

3.210(2)

3.218(1)

3.257(2)

3.306(1)

3.334(1)

3.336(1)

3.466(1)

3.506(2)

3.499(1)

3.618(2)

12] M(1)o-81.

3.228(1)

3.261(3)

3.268(1)

3.280(3)

3.299(2)

3.329(1)

3.325(1)

3.385(3)

3.412(4)

3.435(1)

3.545(4)

[l] H(2)O-81.

3.227(1)

3.27.0(3)

3.279(1)

3.276(3)

3.291(2)

3.359(1)

3.347(1)

3.493(3)

3.508(4)

3.501(2)

3.537(4)

362

Table A4.

0(2)

TETRAHEDRON

Olivine Bond Lengths, cont'd

!!!

(2]

0(2)-M(1)B

2.062(2)

2.075(2)

2.092(2)

2.101(3)

2.122(2)

2.106(2)

2.130(2)

2.091(2)

2.173(4)

2.166(3)

2.308(6)

(I]

0(2)-M(2).

2.041(3)

2.057(3)

2.071(3)

2.081(4)

2.110(2)

2.144(3)

2.120(2)

2.309(4)

2.278(6)

2.308(4)

2.346(8)

0(2)-S'B

1.663(3)

1.656(3)

1.659(3)

1.652(4)

1.655(2)

1.656(4)

1.665(2)

1.656(3)

1.643(5)

1.630(5)

1.665(8)

1.957(1)

1.966(1)

1.978(1)

1.984(2)

2.002(1)

2.003(1)

2.011(1)

2.037(1)

2.067(2)

2.068(2)

2.157(4)

(I]

(1)

M(1)B-M(l)B

2.955(1)

2.997(2)

3.000(1)

3.022(2)

3.050(3)

3.086(1)

3.073(1)

3.193(2)

3.234(2)

3.244(1)

3.392(2)

(2]

M(1)B-M(2).

3.632(1)

3.650(2)

3.669(1)

3.679(2)

3.707(2)

3.734(1)

3.730(1)

3.882(2)

3.902(2)

3.910(1)

3.982(3)

(2]

H(1)B-S'B

2.681 (1)

2.703 (2)

2.720(1)

2.733(2)

2.768 (2)

2.750(1)

2.769 (1)

2.697 (2)

2.774 (2)

2.779(1)

2.978(3)

(I]

M(2) .-SiB

3.270(2)

3.265(2)

3.302(2)

3.304(2)

3.344(2)

3.340(2)

3.359(2)

3.426(2)

3.461(3)

3.473(2)

3.624(4)

2.418(5)

0(3)

TETRAHEDRON

ui

0(3H{(1)B

2.102(2)

2.141(2)

2.166(2)

2.181(3)

2.230(2)

2.190(2)

2.229(2)

2.120(2)

2.235(4)

2.216(3)

Il]

0(3)-M(2)B

2.178(2)

2.221(3)

2.224(2)

2.272(3)

2.293(2)

2.305(2)

2.307(2)

2.411(3)

2.428(4)

2.414(3)

2.453(6)

Il]

0(3)-M(2).

2.051(2)

2.067(3)

2.072(2)

2.058(3)

2.069(2)

2.139(2)

2.113(2)

2.289(3)

2.299(4)

2.303(3)

2.390(6)

(I]

0(3)-S'B

1.641(2)

1.636(3)

1.637(2)

1.633(3)

1.636(1)

1.632(2)

1.629(2)

1.640(2)

1.622(4)

1.645(3)

1.642(5)

•

1.993(1)

2.016(1)

2.025(1)

2.036(2)

2.057(1)

2.066(1)

2.070(1)

2.115(1)

2.146(3)

2.144(1)

2.226(3)

3.306(1)

3.334(1)

3.336(1)

3.466(1)

3.508(1)

3.499(1)

3.618(2) 3.911(3)

(1)

M(1)B-M(2)B

3.138(1)

3.210(2)

3.218(1)

3.257(2)

(I]

M(1)B-M(2)A

3.585(1)

3.585(2)

3.616(1)

3.598(2)

3.621(2)

3.655(1)

3.659(1)

3.742(2)

3.788(2)

3.783(1)

(I]

M(l)B-SiB

2.681(1)

2.703(2)

2.720(1)

2.733(2)

2.768(2)

2.750(1)

2.769(1)

2.697(2)

2.774(2)

2.779(1)

2.978(3)

ui

M(2)B-M(2).

3.814(1)

3.869(2)

3.875(1)

3.901(2)

3.936(2)

3.969(1)

3.964(1)

4.045(2)

4.104(2)

4.117(1)

4.299(2)

(I]

M(2)B-SiB

2.741(2)

2.799(2)

2.803(1)

2.836(2)

2.870(2)

2.889(1)

2.888(1)

3.015(2)

3.046(3)

3.026(2)

3.061(4)

(I]

M(2).-"B

3.257(1)

3.284(2)

3.294(1)

3.299(2)

3.320(2)

3.381(1)

3.358(1)

3.578(2)

3.592(2)

3.594(1)

3.677(3)

3.392(2)

HETAL-MET~ H(1)B-M(l)B

2.955(1)

2.997(2)

3.000(1)

3.022(2)

3.050(3)

3.086(1)

3.073(1)

3.193(2)

3.234(2)

3.244(1)

M(1)B-M(2)B

3.138(1)

3.210(2)

3.218(1)

3.257(2)

3.306(1)

3.334(1)

3.336(1)

3.466(1)

3.508(1)

3.499(1)

3.618(2)

M(1)B-5iB

2.681(1)

2.703(2)

2.720(1)

2.733(2)

2.768(2)

2.750(]J

2.769(1)

2.697(2)

2.774(2)

2.779(1)

2.978(3)

H(2)B-S'B

2.741(2)

2.799(2)

2.803(1)

2.836(2)

2.870(2)

2.889(1)

2.888(1)

3.015(2)

3.046(3)

3.026(2)

3.061(4)

M(2).-M(1)B

3.632(1)

3.650(2)

3.669(1)

3.679(2)

3.707(2)

3.734(1)

3.730(1)

3.882(2)

3.902(2)

3.910(1)

3.982(3)

M(2).-M(2)

3.814(1)

3.869(2)

3.875(1)

3.901(2)

3.936(2)

3.969(1)

3.964(1)

4.045(2)

4.104(2)

4.117(1)

4.299(2)

M(1)B-H(2)

3.585(1)

3.585(2)

3.616(1)

3.598(2)

3.621(2)

3.655(1)

3.659(1)

3.742(2)

3.778(2)

3.783(1)

3.911(3)

51-51

3.586(2)

3.634(2)

3.646(2)

3.681(3)

3.727(2)

3.732(2)

3.740(1)

3.767(2)

3.832(3)

3.860(2)

4.116(4)

363

Table

AS.

Olivine Bond Angles

~TRAHEDRON (1) 0(1)-'1-0(2)

109.5

114.1(2)

114.0(2)

113.5(2)

112.8(2)

112.4(1)

113.5(2)

112.6(1)

115.8(2)

114.2(3)

114.5(2)

109.8(5)

[2) 0(1)-51-0(3)

109.5

116.4(1)

116.1(1)

116.0(1)

115.7(1)

115.7(1)

115.8(1)

115.4(1)

114.5(1)

113.6(2)

114.2(1)

115.8(3)

[2] 0(2)-51-0(3)·

109.5

101.3(1)

102.0(1)

102.5(1)

102.4(1)

103.0(1)

102.3(1)

103.2(1)

102.4(1)

104.8(3)

103.7(2)

104.2(3)

(1] 0(3)-S1-0(3)a

109.5

105.2(2)

104.8(2)

104.7(2)

106.2(2)

105.7(1)

105.6(2)

105.7(1)

105.8(1)

104.8(3)

105.2(2)

105.7(4)

109.5

109.1(1)

109.2(1)

109.2(1)

109.2(1)

109.2(1)

109.2(1)

109.2(1)

109.2(1)

109.3(1)

109.2(1)

109.2(2)

[21 0(1)-M(1)-0(3)b

90.0

84.9(1)

84.9(1)

85.0(1)

85.1(1)

84.6(1)

85.8(1)

85.2(1)

86.9(1)

85.5(2)

85.6(1)

84.4(2)

[21 O(l)-M(l)-O(3')

n~

H.1W

95.1(1)

95.0(1)

94.9(1)

95.4(1)

94.2(1)

94.8(1)

93.1(1)

94.5(2)

94.4(1)

95.6(2)

[2) 0(1)_M(1)_0(2)b

~O

m,2W

86.5(1)

87.0(1)

86.4(1)

86.3(1)

8'.7(1)

86.5(1)

83.1(1)

84.3(2)

84.4(1)

84.3(2)

M(I)

OCTAHEDRDN

[2) 0(1)-M(1)-0(2')

n~

".8W

93.5(1)

93.0(1)

93.6(1)

93.7(1)

94.3(1)

93.5(1)

96.9(1)

95.7(2)

[2] 0(2)-H(1)-0(3')

90.0

104.3(1)

105.3(1)

105.8(1)

106.6(1)

107.5(1)

106.9(1)

107.4(1)

104.8(1)

108.1(2)

108.0(1)

113.0(2)

(2] 0(2)-H(1)-0(3)a

9.5.6(1)

95.7(2)

90.0

75.7(1)

74.7(1)

74.2(1)

73.4(1)

72.5().)

73.1(1)

72.6(1)

75.2(1)

71.9(2)

72.0(1)

67.0(2)

90.0

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

90.0(1)

[21 0(1)-M(2)-0(3")

90.0

91.2(1)

H~W

H.1W

91.7(1)

91.5(1)

92.2(1)

91.7(1)

97.8(1)

96.5(1)

95.4(1)

92.3(2)

(21 0(1)_H(2)_0(3)6

'90.0

82.0(1)

M.9W

D.6W

80.6(1)

80.7(1)

79.5(1)

W.3W

74.7(1)

76.5(2)

77.2(1)

80.1(2)

M(2) OCTAHEDRDN

[21 0(2)-M(2)-0(3)

90.0

96.8(1)

%~W

H.1W

96.9(1)

97.2(1)

97.8(1)

H.9W

99.2(1)

99.6(2)

99.7(1)

101.0(2)

[2) 0(2)-M(2)-0(3"')

90.0

89.7(1)

n~w

~.9W

90.0(1)

90.0(1)

89.6(1)

~~W

86.4(1)

85.9(1)

86.6(1)

87.0(2)

(1] 0(3)-H(2)-0(3)&

90.0

73.5(1)

n.4W

71.3(1)

10.2(1)

69.3(1)

68,6(1)

~.'W

6.5.7(1)

63.9(2)

65.5(1)

64.5(2)

[2) 0(3)-M(2)-0(3")

90.0

89.3(1)

U6W

UIW

88.2(1)

87.5(1)

88.7(1)

~.3W

91.6(1)

90.0(1)

89.8(1)

86.9(1)

(1] 0(3 )-H(2)-0(3"')

90.0

107.3(1)

110.7(2)

110.6(1)

112.9(2)

115.0(1)

113.](1)

114.3(1}

110.9(1)

115.9(2)

114.6(2)

121.3(2)

90.0

89.9(1)

89.8(1)

89.9(1)

89.8(1)

89.8(1)

89.B(1)

89.8(1)

89.7(1)

89.7(1)

89.8(1)

90.0(1)

92.8(3)

0(1) TETRAHEDRON [11 M(l).-O(l)-M(l).

90.0

91.4(1)

91.7(1)

91.3(1)

92.0(1)

91.8(1)

91.8(1)

91.4 (1)

93.4(1)

93.3(3)

92.2(2)

[2) M(1).-0(1)-M(2).

90.0

97.5(1)

97.6(1)

97.4(1)

98.3(1)

98.7(1)

96.7(1)

97.6(1)

95.6(1)

96.8(2)

96.0(1)

96.1(2)

[2] M(l)B-0(1)-S1A

125.3

122.2(1)

122.7(1)

122.9(1)

122.8(1)

122.9(1)

124.1(1)

123.4(1)

124.8(1)

123.2(2}

124.2(1)

125.0(3)

P] M(2)B-0(1)-S1A

125.3

119.5(2)

118.2(2)

118.5(2)

116.8(2)

116.2(1)

116.8(2)

117.0(1)

115.6(2)

116.1(3)

117.1(2)

115.0(5)

107.6

108.4(1)

108.4(1)

108.4(1)

108.5(1)

108.5(1)

108.4(1)

108.4(1)

108.3(1)

108.2(1)

108.3(1)

108.3(1)

0(2) TETRAHEDRON 131.8

124.5(1)

124.1(1)

123.6(1)

123.2(1)

122.3(1)

122.9(1)

122.7(1)

123.8(1)

122.5(2)

121.8(1)

117.6(2)

125.3

123.7(2)

122.8(2)

124.2(2)

124.1(2)

124.9(1}

122.5(2)

124.6(1)

118.6(2)

123.1(3)

122.8(1)

128.4(4)

(2) M(1).-0(2)-51.

78.9

91.4(1)

92.2(1)

92.2(1)

92.7(1)

93.4(1)

93.1(1)

92.9(1)

91.3(1)

92.2(2)

93.0(2)

95.7(3)

[1) M(1).-0(2)-M(1).

90.0

91.5(1)

92.5(1)

91.7(1)

92.0(1)

91.9(1)

94.2(1)

92.3(1)

99.5(1)

96.2(2)

97.0(2}

94.6(3)

106.2

107.8(1)

108.0(1)

107.9(1)

108.0(1)

108.1(1)

108.1(1)

108.0(1)

108.0(1)

108.1(1)

108.2(1)

108.3(1)

[2) M(1).-0(2)-M(2) (I)

A

M(2)A-0(2)-S1B

0(3)

TETRAHEDRON

[1) M(I).-0(3)-M(2). [11 M(1).-0(3)-M(2)

A

[11 M(l).-O(3)-". [1) M(2).-0(3)-M(2)

A

90.0

94.3(1)

94.8(1)

94.3(1)

94.0(1)

93.9(1)

95.7(1)

94.7(1)

99.6(1)

98.1(1)

95.9(2)

131.8

119.4(1)

116.9(1)

117.1(1)

116.1(1)

114.7(1)

115.2(1)

114.8(1)

116.1(1)

112.9(2)

113.7(1)

lOS.9(2)

78.9

90.6(1)

90.4(1)

90.2(1)

90.4(1)

90.1(1)

90.8(1)

90.4(1)

90.8(1)

90.5(2)

90.8(1)

92.3(2)

131.8

128.8(1)

128.9(1)

128.8(1)

128.5(1)

128.9(1)

126.5(1)

127.4(1)

118.8(1)

120.5(2)

121.5(1)

125.2(2)

97.5(2)

U] M(2)s-0(3)-S1B

78.9

90.6(1)

91.8(1)

91.8(1)

91.7(1)

92.3(1)

92.8(1)

92.8(1)

94.2(1)

95.4(2)

94.5(1)

94.7(2)

[1] M(2)A-0(3)-Sis

125.3

123.4(1)

124.5(1)

124.9(1)

126.3(2)

126.8(1)

126.9(1)

127.2(1)

130.4(1)

131.9(3)

130.4(2)

130.7(3)

106.2

107.8(1)

107.9(1)

107.8(1)

107.8(1)

107.8(1)

108.0(1)

107.9(1)

108.3(1)

108.1(1)

108,2(1)

108.0(1)

OLIVINES AND SILICATE SPINELS:

Adams, F. D., and R. F. D. Graham (1926) of Mogok, Upper Burma. Trans. Royal

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Fe/Mg

Ternary

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CaCl-Mgo-Sio2.

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Fisher, G. W., and L. G. Medaris, Jr., (1969) Cell dimensions and x-ray curve for synthetic Mg-Fe olivines. Amer. Mineral., 54, 741-753. l'leet, M. E. (1974) Distortions o11vines, clinopyroxenes~ Fleet,

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Comment

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65, 209-217.

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CaO-MgO-Si02-H20

Carnegie

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Inst. Wash.

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Gallitelli, P., .and M. Cola (1954) Sintesi, proprieta, cristallegrafiche e strutturali del compos to C02Si04 {t f.po dell' o Hvtna) , Att!. Accad. NaaL, Lince!. Rend. Classe Sci. Fis. Mat. Nat ., 17, 172-177. Ganguli, D. (1977) 130, 303-318. Geller,

Crystal

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S., and J. L. Durand (1960) Crystallogr., 13, 325-331.

aspects

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Refinement 369

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of the structure

N. Jahrb.

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Miner.

Acta

Abh.,

Ghose, S. (1962) The nature of Mg2+_Fe2+ di.stribution minerals. Amer. Mineral., 47, 388-394. Ghose, S. (1965) Mg2+_Fe2+ distribution Z. Kristallogr., 125, 1-6.

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in some ferromagnesian

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orthopyroxenes.

Ghose, S., F. P. Okamura, C. Wan, and H. Ohashi (1974) Site preference of transition metal ions in pyroxenes and olivine (abstr.). EOS, Trans. Amer. Geophys. Union, 55, 467. Chose, S., and C. Wan (1974) Strong site preference Contr. Mineral. Petrol., 47, 131-140.

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M. T. (1976) Vibrational studies of olivine-type compounds - III. and germanates AIBIIIXIV04' Spectrochim. Acta, 3ZA, 383-395.

Ortho-

Paques-Ledent, M. T., and P. Tarte (1974) Vibrational studies of olivine-type compoundsII: Orthophosphates-arsenates and -vanadates AIBIIXIV04" Spectrochim. Acta, 30A, 673-689. Pauling, L. (1929) The principles determining J. Amer. Chern. Soc., 51, 1010-10Z6.

the structure

Pauling,

L. (1948)

The modern

theory of valency.

Pauling,

L. (1980)

The nature

of silicon-oxygen

Pistorius, C. W. F. T. (1963) SiOZ-HZO and ZnO-SiOZ-HZO Monat., 31-57.

of complex ionic crystals.

J. Chem. Soc., 1948, 1461-1467. bonds.

Amer. Mineral.,

Some phase relations in the systems to high pressures and temperatures.

CoO-SiOZ-HZO, NiON. Jahrb. Mineral.

Pistorius, C. W. F. T., and J. C. A. Boyens (1970) Crystallographic polymorphism of silver chromate and selenate at high pressures Z. anorgan. allgem. Chem., 37Z, Z63-Z67. Pluschkell, W., and H. J. Engell (1968) Ionen- und Elektronen-leitung orthosilikat. Ber. Dtsch. Keram. Ges., 4S, 388. Powell, M., and R. Powell (1974) An olivine-clinopyroxene Mineral. Petrol., 48, 249-Z63.

65, 3Zl-3Z3.

aspects of the and temperatures.

in Magnesium

geothermometer.

Contr.

Presnall, D. C. (1966) The join forsterite-diopside-iron oxide and its bearing on the crystallization of basaltic and ultramafic magmas. Amer. J. Sci., 264, 753-809. Prinz, M., D. V. Manson, P. F. Hlava, and K. Keil (1975) Inclusions in diamonds: garnet lherzolite and eclogite assemblages (abstr.). Intern. Conf. Kimberlites, 267-Z69. 376

Putnis, A. (1979) Electron petrography of high-temperature Rhurn layered intrustion. Mineral. Mag., 43, 293-296. Rager, H. (1977) Electron Phys. Chern. Mineral.,

spin resonance 2, 371-378.

of trivalent chromium

Raj amani , V., G. E. Brown, and C. T. Prewitt Amer. Mineral., 60, 292-299. Ramberg, H., and G. W. DeVore olivines and pyroxenes.

oxidation

(1975)

in olivine from

in forsterite,

Cation ordering

in Ni-Mg olivine.

of Fe2+ and Mg2+

(1951) The distribution Geo1., 59, 193-210.

MgZSi04'

in coexisting

J.

Rao, V. U. S., F. E. Huggins, and G. P. Huffman (1979) Study of Fe-rich superparamagnetic clusters in olivine (Mg,Fe)2Si04 by ~6ssbauer spectroscopy. J. Appl. Phys., 50, 2408-2410. Raymond, M. (1971) Madelung Book, 70, 225-227.

constants

for several

Reiner, D. (1968) Ge4+ - und Si4+-haltige 356, 182-187.

silicates.

Olivinphasen.

Ribouel, P. V., and A. Muan (1962) Phase equilibria MnO-Si02' Trans. A.1.M.E., 224, 27-33.

Carnegie

Zeit. anorgan.

allgem.

Chern.,

in a part of the system flFeO"-

Ricker, R. W., and E. F. Osborn (1974) Additional phase equilibrium system CaO-MgO-Si02' J. Amer. Cer. Soc., 37-133-139. Rickel, C., and A. Weiss (1978) Cation-ordering Z. Naturforsch., 33b, 731-736.

Inst. Wash. Year

in synthetic

data for the

Mg2-xFexSi04-0livines.

Rigby, G. R., G. H. B. Lovell, and A. T. Green (1945) The reversible thermal expansion and other properties of some calciUm ferrous silicates. Trans. Brit. Ceram. Soc., 44, 37-52. Rigby, G. R., G. H. B. Lowell, and A. T. Green (1946) The reversible thermal expansion and other properties of some magnesian ferrous silicates. Trans. Brit. Ceram. Soc., 45, 237-250. Ringwood, A. E. (1956) Melting relationships implications. Geochim. Cosmochim. Acta, Ringwood, A. E. (1958) spinel transition. Ringwood, A. E. 5, 401-412.

(1969)

and some geochemical

Constitution of the mantle - II. Further data on the olivineGeochim. Cosmochim. Acta, 15, 18-29. Phase transformations

Ringwood, A. E. (1972) Phase transformation Lett., 14, 233-241. Ringwood, A. E. (1975) McGraw-Hill.

of Ni-Mg o1ivines 10, 297-303.

in the mantle.

Earth Planet. Sci. Lett.,

of mantle dynamics.

Earth Planet. Sci.

Composition and PetroLogy of the Earth's Mantle.

Ringwood, A. E., and A. Major (1966) Synthesis Earth Planet. Sci. Lett., 1, 241-245.

of Mg2Si04-Fe2Si04

spinel

Ringwood, A. E., and A. F. Reid (1970) Olivine-spinel transformation FeMnGe04, CoMnGe04' J. Phys. Chem. Solids, 31, 2791-2793.

New York:

solid solutions.

in MgMnGe04,

Robinson, K., G. V. Gibbs, and P. H. Ribbe (1971) Quadratic elongation: a quantititative measure of distortion in coordination polyhedra. Science, 172, 567-570. Rocktaschel, G., W. Ritter and A. Weiss (1964) Ternary chalcogenides with group IV-A elements and their olivine structure. Z. Naturforsch. 19b, 958. Roedder,

E. W. (1951)

The system K20-Mg0-Si02.

Amer. J. Sci., 249, 81-130,

224-248.

Roedder, E.W. (1976)·Petrologic data from experimental studies on crystallized silicate melt and other inclusions in lunar and Hawaiian olivine. Amer. Mineral., 61, 684-690. Roeder, P. L. (1974) Activity Earth Planet. Sci. Lett.,

of iron and olivine 23, 397-410.

solubility

in basaltic

liquids.

Roeder, P. L., and E. F. Osborn (1966) Experimental data for the system MgO-FeQ-Fe20r CaA12Si20 -Si02 and their petrologic implications. Amer. J. Sci., 264, 443. 4 Roy, D. M. (1956) of merwinite.

Subsolidus data for the join Ca2Si04-CaMgSi04 Min. Mag., 31, 187-

Roy, D. M., and R. Roy (1955) Synthesis and stability MgQ-Al203-Si02-H20. Amer. Mineral., 40, 147.

and the stability

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Runciman, W. A., D. Sengupta, and J. T. Gormley (1973) The polarized in silicates. II. Olivine. Amer. Mineral., 58, 451-456.

spectra

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Runciman, W. A.,. D. Sengupta, and J. T. Gormley (1974) The polarized silicates: II Olivine: a reply. Amer. Mineral., 59, 630-631.

spectra

of iron in

Sack, R. O. (1980) orthopyroxenes

Some constraints on the thermodynamic mixing properties and olivines. Contr. Mineral. Petrol., 71, 257-269.

Sahama, Th. G. (1961) (Eastern Congo).

Thermal metamorphism of the volcanic Finland C0mmission Geologique Bull.,

of Fe-Mg

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Sahama , Th. G., and K. Hytonen (1957) Kirschsteinite, a natural analogue to synthetic iron monticellite, from the Belgium Congo. Mineral. Mag., 31~ 698. Sarver, J. V., and F. A. Hummel the system Zn2~i04-Mg2Si04'

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temperature

in

Saxena, S. K. (1969) Silicate solid solutions and geothermometry. 2. Distribution of Fe2+ and Mg2+ between coexisting olivine and pyroxene. Contr. Mineral. Petrol., 22, 147-156. Schairer, J. F. (1942) The system CaQ-FeO-Al20rSi02: 1. Results ments on five joins. J. Amer. Cer. Soc., 25, 248-252.

of quenching

experi-

Schairer, J. F., and E. F. Osborn (1950) The system CaO-MgQ-FeO-Si02: I, preliminary data on the join CaSi03-MgO-FeO. J. Amer. Cer. Soc., 33, 160-167. Schairer, J. F., and K. Yagi Bowen Vol., 471.

(1952)

The system FeO-A1203-Si02'

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of

Sc~itz-Dumont, 0., H. Fendel, M. Hassanein, and H. Weissenfeld (1966) Farbe und konstitution bei anorganischen Feststoffen, 14. Mitt. Die lichtabsorption des zweiwertigen k~pfers in oxidischen wirtsgittern. Mh. Chem., 97, 1660-1695. Schock, R. N., B. Olinger, and A. Duba (1972) Additional data on the compression olivine to 140 kilobars. J. Geophys. Res., 77, 383-384. Schubert, G., D. A. Yuen, and D. L. Turcotte (1975) Role of phase transitions dynamic mantle. Geophys. J. Royal Astron. Soc., 42, 705-735.

of

in a

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ionic radii in oxides and

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(1974)

MBssbauer

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Minor element distribution

Singh, H. P., and G. Simmons (1976) X-ray determination olivines. Acta Crystallogr., A32, 771-773.

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in olivine.

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The crystal structure of y-dicalcium

of rock-forming

minerals

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J. V. (1971) Minor elements in Apollo 11 and Apollo 12 olivine and plagioclase. [Toa. 2nd Lunar Sai. Conf., Geochim. Cosmochim. Acta, Suppl. 2, 1, 143-150.

Smith,

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story.

Presidential

Smyth, D. M., and R. L. Stocker (1975) Point defects and nonstoichiometry Phys. Earth Planet. Inst., 10, 183. Smyth, J. R. (1975) 60, 1092-1097.

High-temperature

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Amer.

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Smyth, J. R., and R. M. Hazen (1973) The crystal structures of forsterite and hortonolite at several temperatures up to 900"C. Amer. Mineral., 58, 588-593. Sockel, H. G. (1974) Defect structure and electrical conductivity of crystalline ferrous silicate. In, Defeats and Transport in Qxides (Ed. N. S. Seltzer and R. I. Jaffee), New York: Plennum Press, 341 p. Steele, 1. M., J. J. Pluth, and J. Ito (1976) Crystal structure of synthetic LiScSi04' Olivine-comparison with Mg2Si04 and LiFeP04 (abstr.). Amer. Crystallogr. Assoc. Summer Mtg., 68. Stewart, R. F., M. A. Whitehead, and G. Donnay (1980) in low quartz. Amer. Mineral., 65, 324-326.

The ionicity

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Stocker, R. L., and D. M. Smyth (1978) Effect of enstatit~ activity and oxygen partial pressure on the point defect chemistry of olivine. Phys. Earth Planet. Inst., 16, 145-156. Strunz, H., and P. Jacob (1960) Mineral. Abhandl., 78-79.

Germanate mit Phenacit-und

Olivinstruktur.

N. Jahrb.

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transformations

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der Verbindungen B9, 241-264.

Zn2Ti04,

Zn2Sn04'

'T Hart, J. (1978a) The structural morphology Canadian Mineral., 16, 175-186.

of ol~vine.

T. A qualitative

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of olivine.

IT. A quantitative

379

olivine Geochim.

Ni2Si04

derivation.

derivation.

Thielo, E. (1941) Uber df,e Isotyp1e setzung MeLi[P04) und Silikaten 29, 239. Tokody, L. (1928) 51-56.

The binary

zwf.schen Phosphaten der Allgemienen ausammender 01ivin~nticellit-Reihe. Naturwissenschaften,

system; Mn2Si04-Ca2Si04'

Z. anorg.

allgem.

Chem.,

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Zoned olivines and their petrogenetic

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significance.

oxide minerals

Mineral.

at high-

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dis-

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de

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deWaal, S. A., and L. C. Calk (1973) Nickel minerals from Barberton, South Africa: VI. liebenbergite, a nickel olivine. Amer. Mlneral., 58, 733-735. I

Walsh, D., G. Donnay, and J. D. H. Donnay (1974) Jahn~Teller effects in ferromagnesian minerals. Bull. Soc. fro Mineral. Crist., 97, 170-183. Walsh, D., G. Donnay, and J. D. H. Donnay (1976) olivine. Canadian Mineral., 14, 149-150.

Ordering

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during

Wager, L. R., and R. L. Mitchell Cosmochim. Acta, 3, 217,

Geochim.

(1953)

Warner, R. D. (1973) Liquidus relations and their petrologic significance.

Trace elements

in Hawaiian

lavas.

in the system CaO-MgO-Si02-H20 Amer. J. Sci., 273, 925-946.

strong

°

at 10 kb PH 2

Warner, R. D., and W. C. Luth (1973) Two-phase data for the join monticellite (CsMgSi04)forsterite (MgzSi04): experimental results and numerical analysis. Amer. Mineral., 58, 998-1008. Waseda, Y., and J. M. Toguri (1977) The structure of molten CaO-Si02 and MgO-Si02. Metal Trans. B., 8B, 563-568. Waseda, Y., and J. M. Toguri Trans. B., 9B, 595-601.

(1978)

The structure

binary silicate

of the molten FeD-SiOZ

systems

system.

Metal.

Watson, E. B. (1979) Calcium content of forsterite coexisting with silicate liquid in the system Na20-CaO-MgO-Al203-Si02' Amer. Mineral., 64, 824-829.

C.

Weeks, R. A., J. C. Pigg, and B, Finch (1974) Charge-transfer spectra in synthetic forsterite (Mg2:Si04)' Amer. Mineral., 59, 1259-1266. 380

of Fe3+ and Mn2+

Weir,

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C. E., and A, van Valkenburg (1960) beryllia compounds with RZ"3oxides.

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(1960)

Zur Kenntnis

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Four new structure

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Iron Steel Inst. J.,

spectra

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Factors affecting element ratios in the crystallization Cosmochim. Acta, 31, 2275-2288.

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in a random close-packed

(1973) Water 58, 508-516.

contents

structure.

of some nominally

J.

Non-.

anhydrous

Will,

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Will,

G., and G. Nover (1979) bution in olivine. Phys.

Influence of oxygen partial Chem. Minerals, 4, 199-208.

Williams, R. J. (1971) Reaction constants 900' and 1300': experimental results. Wood,

B. J. (1974) 244-248.

Crystal

field spectrum

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pressure

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geothermometer:

B. J., and D. G. Fraser (1976), Bl.ementarg England: Oxford University Press.

Thermodynamics

Wyderko, M., and E. Mazanek (1958) The mineralogical olivines. Mineral. Mag., 36, 955-961.

Amer. Mineral.,

a discussion.

for

59,

Contr.

Geologists.

characteristics

Wyllie, P. J. (1960) The system CaO-MgO-FeO-S~02 and its bearing basic and basic rocks. Mineral. Mag., 28, 459_470. Yagi,

on the Mg/Fe distri-

Oxford,

of calcium~iron

on the origin of ultra-

T., Y. Ida, Y. Sato, and S. Aktmoto (1975) Effect\of hydrostatic pressure on the lattice parameters of FeZSi04 olivine up to 70 kbar. Phys. Earth Planet. Int., 10, 348-354.

Yagi, T., F. Marumo, and S. Akimoto (1974) Crystal structures Fe2Si04 and Ni2Si04' Amer. Mineral., 59, 486-490. Yang, H. (1973) New data or forsterite 58, 343-345.

and monticellite

Yoder, H. S., Jr. (1952) The Mg0-Al203-Si02-H20 facies. Amer. J. Sci., Bowen vol., 569.

of spinel polymorpbs

solid solutions.

system and the realted

of

Amer. Mineral.,

metamorphic

Yoder, H. S., Jr. (1968) Akermanite and related melilite~bearing assemblages. Tnst. Wash. Year Book, 66, 471-477.

Carnegie

Yoder, H. S., Jr., and T. G. Sahama (1957) Mineral., 42, 475-491.

Amer.

Olivine

Ziera, S., and S. S. Hafner (1974) The location Earth Planet. Sci. Lett., 21, 201-208.

x-ray

determinative

of Fe3+ ions in forsterite

Zoltai, T. (1965) Stereoscopic Draiainqe of Polyhed:t>al Mineral-St:ructu:Pe apolis, Minnesota: University of Minnesota, 84 p. 381

curve.

(Mg2Si04)

Models.

Minne-

Chapter 12 MISCELLANEOUS ORTHOSILICATES

I.A. Speer & P.H. Ribbe In this chapter we present brief descriptions not discussed

elsewhere

known to fit into the arbitrary the first edition

of minerals

which are

in this volume and whose crystal structures confines

of this volume

are

that were set in the preface

(Ribbe, 1980).

Specifically,

of

those

in which Si04 groups are not polymerized to other groups by corner-sharing nor are they polymerized to other tetra-

minerals Si0 4 hedral

are included

groups containing

cations such as Be, B, Al or Zn.

In order that this chapter be second edition,

usable

we have, in addition,

species names of those minerals through 11 as isostructural,

as an index to this the

listed alphabetically

which are classified

polymorphous

all the

in Chapters

or homologous

2

with the major

'or t ho s f lLca t e groups. We make no claim to have found all the known silicates which this description, Strunz

but we have searched

(1977), Ramdohr

and Strunz

the lists of Povarennykh

(1980) and Fleischer

fit

(1972),

(1980, 1981).

REFERENCES

Fleischer, M. (1980) 1980 Glossary of Mineral Species. Record, P. O. Box 35565, Tucson, Arizona, 192 p. Fleischer, M. (1981) U. S. Geological

The Ford-Fleischer Survey

Open-File

Mineralogical

File of Mineralogical Report 81-1169

A. S. (1972) Crystal Chemical Classification Volume 1. Plenum Press, New York, 458 p.

Povarennykh,

References.

(microfiche).

of Minerals,

Ramdohr, P. and H. Strunz (1980) Klockmanns Lehrbuch der Mineralogie, 16th edition, updated to 1980. Ferdinand Enke Verlag, Stuttgart, 931 p. Ribbe, P. H., editor 381 p.

(1980)

Orthosilicates.

Reviews in Mineralogy

Strunz, H. (1977) Mineralogische Tabellen, 6th edition. Verlagsges. Geest & Portig K. G., Leipzig. 383

Akad.

5,

• AFWILLITE,

Ca3(Si030H)2·2H20. Cc; a

Monoclinic, Afwillite shale enclaves

occurs

=

in the Dutoitspan

with calcite

it is of most interest

The crystal hydrogen prised

structure

atoms were

marbles

because

of afwillite

S = 134.9°;

and bultfonteinite

Mine kimberite,

1925) and in the contact metamorphic However,

A;

16.278, b = 5.6321, c = 13.236

in cavities

South Africa

Z

=

4.

in dolerite

and

(Parry and Wright,

of the Scawt Hill dolerite,

Ireland.

of its being one of the cement minerals. was determined

located by Malik and Jeffery

by Megaw

(1976).

(1952) and the

The structure

is com-

of isolated

(Si0 0H) tetrahedra sharing corners and edges with irregular 3 Ca07 polyhedra; together they form sheets of composition [Ca Si 0 16+ parallel to 3 2 4 (101). The sheets are joined by a few Ca-O-Si and hydrogen bonds, leading to a

well developed

(101) cleavage.

@ Oxygen @ Calcium • Silicon S Hydrogen

The crystal (1976).

structure

of afwillite

projected

on (010).

Malik, K.M.A. and J.W. Jeffery (1976) A re-investigation afwillite. Acta Crystallogr. B32, 475-480. Megaw, H.D. (1952) The structure logr. 5, 477-491.

of afwillite,

From Malik and Jeffery

of the structure

Ca3(Si030H)2·2H20.

of

Acta Crystal-

Parry, J. and Wright, F.F. (1925) Afwillite, a new hydrous calcium silicate from the Dutoitspan Mine, Kimberley, South Africa. Mineral. Mag. 20, 277-286.

384

• ALLEGHANYITE,

See DATOLITE,

• BAKERITE .

A garnet; see Chapter

2.

A garnet;

2.

see Chapter

2+

this chapter.

this chapter.

I4l/acd; a = 9.41, c = 18.67 A; Z = 8.

(Ca,Mn)

2+

3+ . Mn14S~024'

I4l/acd; a = 9.44, c = 37.76; Z = 8.

Tetragonal, Braunite

10.

3+. Mn6 S~012'

Tetragonal, • BRAUNITE-II,

see Chapter

this chapter.

See section on URANYL SILICATES,

• BOLTWOODITE.

Mn

of chondrodite;

See section on URANYL SILICATES,

• Beta-URANOPHANE.

• BRAUNITE,

The Mn-analog

2Mn2Si04 'Mn(F ,OH) 2'

can be found in manganese

ores formed at low temperatures

as well

as in Mn-rich

rocks over a range of metamorphic grades in both regional and cori. 2+ 3+ 3+ tact metamorph~sm. It has the general formula (Mn ,Ca,Mg)l±x(Mn ,Al,Fe )6±2x

Sil±x012

(Abs-wurmbach , 1980).

depends on the coexisting ture of equilibration

mineral

ferric

(Seifert and Dasgupta, studies,

concluded

silica content

between

The structure and Araki packing

analyses

of other braunites

(1967). 3 3 the Mn +Mn +!

compounds

octahedra

chemistry

1981);

is in Fe which and tempera-

95% of the iron is

(1959a,b), on the basis of experi-

content of braunite

2 of braunites

this.

can vary between

and subsequent A braunite

has been designated

experimental

with half the

braunite-II

by DeVilliers

Rather than a complete solid solution, DeVilliers 2 4 Mn +Si + coupled substitution produces discrete,

(1975) ordered

Mn20

(hausmannite) and 3Mn 0 ·MnSi0 (braunite). 3 2 3 3 of braunite was determined by DeVilliers (1975) and Moore

(1976) and is related to that of fluorite.

of edge- and corner-shared

a stacking

Muan

1980) failed to confirm

and Herbstein suggests

1982).

that the Si0

and 40 wt %, but chemical

work (Abs-Wurmbach,

chemical variation bulk-rock

(Dasgupta and Manickavasagam,

mental

o

The largest assemblage,

distorted

It is comprised

of a

Mn(l) cubes, Mn(2), Mn(3), Mn(4)

and Si04 tetrahedra. Moore and Araki (1976) describe the structure as of two types sheets along [001]: the A sheet is made up of Mn(2) and

Mn(3) octahedra

arranged

in a checkerboard

the B sheet is checkerboard

by corner- and edge-sharing

of corner- and edge-sharing

(figure a),

Mn(l) cubes, Mn(4) octa-

hedra and Si04 tetrahedra (figure b). The stacking is ... [AB)4'" The structure of braunite-II is unknown, but DeVilliers (1975) suggests comprised

of two Mn20 cells plus an braunite cell along 3 (1976) suggested a similar arrangement with the notation 385

[001].

it is

Moore and Araki

... [AA'AA'AB]4

..•

• BRAUNITE,

continued

b

a

(a) The A sheet in the braunite crystal structure. (b) The B sheet. Note tetrahedral, octahedral, and cubic coordination for Si, Mn(4) and Mn(l), respectively. From Moore and Araki (1976), Figs. lA and 2A). 2 3 ~b~~wurmbach, I. (1980) Miscibility and compatibility of braunite, Mn +Mn +086 Si04, in the system Mn-Si-O at 1 atm in air. Contr. Miner. Petrol. 71, 393399. Dasgupta, H.C. and R.M. Manickavasagam (1981) Chemical and X-ray investigation of braunite from the metamorphosed manganiferous sediments of India. N. Jahrb. Mineral. Abh. 142, 149-160. DeVilliers, J.P.R. (1975) The crystal structure of braunite with reference its solid solution behavior. Am. Mineral. 60, 1098-1104. and F.H. Herbstein (1967) Distinction -----group. Am. Mineral. 52, 20-30.

between

two members

to

of the braunite

Moore, P.B. and T. Araki (1976) Braunite: Its structure and relationship to bixbyite and some insights on the genealogy of fluorite derivative structures. Am. Mineral. 61, 1226-1240. Muan, A. (1959a) Phase equilibria Am. J. Sci. 257, 297-315. --44,

(1959b) Stability 946-960.

relations

in the system manganese among some manganese

Seifert, F. and H.C. Dasgupta (1982) in braunite. N. Jahrb. Mineral.

oxide - Si0

minerals.

A note on the Mossbauer Mh., 11-15.

386

2

in air.

Am. Mineral.

spectrum

of 57Fe

.BREDIGITE,

Cal.75MgO.25[Si04]'

Orthorhombic,

P2nn; a = 10.909, b = 18.34, c = 6.739 A; Z = 2.

Bredigite occurs in calcsilicate in the spurrite-merwinite information

regarding

rocks which have been contact-metamorphosed

facies and, more commonly, in slags.

bredigite

is based on material

Much of the

from slags and synthetic

bredigite. Based on an occurrence a calcium orthosilicate and Vincent,

1948).

in slag, bredigite was originally

Subsequent

studies of synthetic bredigite

Biggar, 1971; Lin and Foster, 1975) and microprobe Scawt Hill, Ireland

(Gutt, 1961;

analyses of bredigite

(Joesten, 1974) show that the magnesium

ranging between Cal.67MgO.33Si04

The figure below illustrates of a slag bredigite

to be

from

(Midgley and Bennett, 1971; Sarkar and Jeffery, 1978) and

Christmas Mtns., Texas compositions

considered

in which Ca can be replaced by Mg, Mn and Ba (Tilley

of composition

consists of edge-sharing and has symmetry of Pmcb. hedra lowers the symmetry

is essential with

and Cal.8MgO.2Si04'

an ideal configuration

on which the structure

ca24.6Bal.2Mg4.8Mnl.4[Si04J16l~s9b~~e~.

isolated polyhedra

of ideal formula

X

4It

X2Y4 M [T 0 ]4 4

But ordering of Ba and Mn and tilting of the tetrato P2nn and the actual structural

formula is (X10,X6)

X~Yioy8y8y7M6[T40414 with Ba present in Xlo and Mg+Mn in M6.

Structure ideal for the (001) projection of the Pmcb arrangement to which bredigite is related. The symmetry elements and the unit cell are outlined. The nonequivalent atom positions are labelled, and the octahedral sites are stippled. In the real structure the tetrahedra are tilted substantially (see inset, lower right). After Moore and Araki (1976, Figs. 2 and 3).

387

• BREDIGITE,

continued

Biggar, G.M. (1971) Phase relationship of bredigite (CaSMgSi3012) and of the quaternary compound (Ca6MgAlsSi021) in the system CaO-MgO-A1203-Si02' Cement Concr. Res. 1, 493-513. Gutt, W. (1961)

A new calcium magnesiosilicate.

Nature 190, 339-340.

Metasomatism and magmatic assimilation at a gabbro-limestone contact> Christmas Mtns.> Big Bend region> Texas. Ph.D. thesis,

Joesten,

R. (1974)

Calif. Inst. Tech., Pasadena,

Calif. 397pp.

Lin, H.C. and W.R. Foster (1975) Stability 3Si02)' J. Am. Ceram. Soc. 58, 73.

relations

(5CaOoMgO'

of bredigite

Midgley, H.G. and M. Bennett (1971) A microprobe analysis of larnite and bred igite from Scawt Hill, Larne, N. Ireland. Cem. Concr. Res. 1, 413-418. Moore, P.B. and T. Araki (1976) The crystal structure of bredigite and the genealogy of some alkaline earth orthosilicate. Am. Mineral. 61, 74-87. Sarkar, S.L. and J.W. Jeffery (1978) Electron microprobe analysis bredigite-larnite rock. J. Am. Ceram. Soc. 61, 177-178.

of Scawt Hill

Tilley, C.E. and H.C.G. Vincent (1948) Occurrence of an orthorhombic hightemperature form of Ca2Si04 (bredigite) in the Scawt Hill contact zone and as a constituent of slags. Mineral. Mag. 28, 255-271 .

See section on SILICATE APATITES>

• BRITHOLITE. • BRITHOLITE-Y.

• BULTFONTEINITE, Triclinic, y

=

this chapter .

See section on SILICATE APATITES>

this chapter .

Ca4[Si02(Ofu~)2]2oF202H20.

pI.

a = 10.992, b = 8.185, c = 5.671 A; a

93°57', S

91°19' ,

89°51'; Z = 2. Bultfonteinite

Dutoitspan

occurs with afwillite

Mine kimberlite,

tact metamorphic

South Africa

marbles of Crestmore,

The structure of bultfonte1nite by Megaw and Kelsey (1963).

in the

California.

was suggested

to be related to afwillite

(1955) and does contain similar elements as shown by McIver

The structure

coordinated

and calcite in enclaves

(Parry et al.> 1932) and in the con-

is comprised

of isolated

[Si02(OH~)21

tetrahedra

and 7-

Ca atoms which share edges to form double columns of composition

[Ca4Si20 ]8+ parallel to (100). Similar double columns are present in afwillite, 4 but they are joined by sharing edges to give the sheets (See the figure). These columns are linked by Ca-O-Ca, Ca-O-Si and hydrogen

bonds as well as Ca-F-Ca bonds.

Figure on next page. McIver, E.J. (1963) The structure Crystallogr. 6, 551-558.

of bultfonteinite,

Ca4Si2010F2H6'

Acta

Megaw, H.D. and C.H. Kelsey (1955) An accurate determination of the cell dimensions of bultfonteinite, Ca4Si20l0H6F2' Mineral. Mag. 30, 569-573. Parry, J., A.F. Williams and F.H. Wright. (1932) On bultfonteinite, bearing hydrous calcium silicate from South Africa. Mineral. 388

a new fluorineMag. 23, 145-162.

eBULTFONTEINITE,

continued

r

I

fi}

a

I

p

til

~

o

Ca

•

Si

o

0

I

Lo

'\J~

b

(a) Arrangement of the (Ca Si204)8+ strips in bultfonteinite. (b) Arrangement of 4 the (Ca4Si204)8+ strips in afwillite. In this case they are ioined together to form infinite sheets with composition (Ca Si 0 )6+. From McIver (1963). Fig. 7. 3 2 4

2 (ce,ca)9(Mg,Fe+ )Si (0,OH,F)28' 7 Trigonal, R3c; hexagonal cell: a

e CERITE,

Cerite occurs associated

with alkali syenites

and is notably

Ce-rich.

with whitlockite, sidered

in pegmatites

of whitlockite,

below on SILICATE

Z = 6.

It is enriched

or ~+Ln8si7028'3H20.

veins

in light REE's

apatites elements

cerite can be con-

Based on the crystal

(1975) suggest

The compositional

to the RE-silicate

A;

carbonate-bearing

(1968) has shown that cerite is isotypic

Calvo and Gopal

of the rare earth and divalent section

and granites.

Keppler

(Ca,Mg,Fe+2)3RE7Si70270H'H20. relationship

10.78, c = 38.03

and Ito (1968) has shown that synthetic

as M;+Ln7si70270HoH20

structure

=

and hydrothermal,

the former, namely

range for cerite and its

(britholites)

in terms of ionic radii

is shown in the figure.

APATITES.

Co

F.

See also the

Mo

Co

LoM~9N;

'0'

Compositional cerites.

stability

Abscissa

is

range of

the ionic

o

See section

eHENRITERMIERITE,

with

contains

garnet

Anti-Atlas,

(cf. Chapter 2,

a small amount of ferric iron

ca2.97Mn~48A10.S4Fe~~06Sil.9309.8S·2.0S

Aubry et at.

of the garnet

(1969) determined

H20 that the structure

structure.

Aubry, A., Y. Dusausoy, A. Laffaille and J. Protas (1969) Determination et etude de la structure cristalline de l'henritermiertie, hydrogrenat de Symetrie quadratique. Bull. Soc. Fr. Mineral. Cristallogr. 92, 126-133. Gaudefroy, C., M. Orliac, F. Permingeat and A. Parfenoff (1969) L'henritermierite, une nouvelle espece minerale. Bull. Soc. Fr. Mineral. Cristallogr. 92, 185-190.

See DUMORTIERITE,

eHOLTITE.

eHOMILITE,

this chapter.

ca2Fe2+BZ02(Si04)2'

Monoclinic, Homilite

P2l/a;

occurs

a = 9.67, b = 7.57, c = 4.74 A; S = 90 22'; Z = 2. 0

in nepheline

syenites

of the Langesundfiord,

Norway.

It can be considered

the boron analogue of gadolinite, (y,RE)3+Fe2+Be202(Si04)2' 2 by the coupled substitution Ca+ + B3+ = (Y,RE)3+ + Be2+ or an anhydrous dato2 lite charge balanced by the addition of Fe + Natural homilites have significant solid solutions

eHORTONOLITE,

eHUMITE,

with GADOLINITE.

(Fe,Mg)Si0 . 4

3Mg2Si04'Mg(F,OH)2'

See GADOLINITE

An olivine;

see Chapter

(this chapter)

11.

One of the humite mineral 398

for references.

series;

see Chapter

10.

• HUTTONITE,

ThSi0 . 4

Cylindrical Imogolite

An actinide

symmetry,

the electron

microscope

K

tubes, each ~20 22-23

K

normal

deduced

the gibbsite

silicate

deposits.

found in volcanic

Cradwick

that the mineral

from a gas chromatographic

they proposed

octahedral

K

= 10, 11 or 12.

aluminum

pyroclastic

to observe

4.

et al.

occurs

A

repeat

replaces

site" in gibbsite, in gibbsite

sheet to form a tube.

data were

tested against

concluded

that the 23

a

A

thereby

in imogolite

models

of several

b dimension

They

of the [Si04] groups surrounding

for the shortening

and also the curling

See the figures below.

cylindrical interaxial

separation.

"the three hydroxyl

A

of fine

along the tube axis and

recognition

accounting

to 8.4

ash

(1972) used

in bundles

to the tube axis, i.e., the center-to-center

group with which a vacant

hydrous

see Chapter

in diameter with repeats of 8.4

the structure

of the 8.6

C2nh' with n

is a gel-like

soils and other weathered

orthosilicate;

of

X-ray intensity

diameters,

and it was

fit best. (a) Postulated relationship between a structural unit of imogolite and that of gibbsite. SiOH groups which would lie at the cell corners in imogolite have been omitted from the diagram. A reflection plane (solid arrow, left) and rotationreflection planes (broken arrows) are indicated. (b) Curling of the gibbsite sheet induced by

b Gibb,lt. ~ I---Imogolit. l'w/;;--->!

contraction

of one

sur-

face to accommodate Si030H tetrahedra: projection along the axis (imogolite c). From Chadwick et al , (1972, Fig. 1). Chadwick, P. D. G., V. C. Farmer, J. D. Russell, C. R. Masson, K. Wad a and N. Yoshinaga (1972) Imogolite, a hydrated aluminum silicate of tubular structure. Nature Phys. Sci. 240, 187-189.

399

e JERRYGIBBSITE,

Mn (SiO 4) I, (OH) 2 . 9

Pbmn or P2lnb; a = 4.86, b = 10.79, c = 28.30 A; Z = 4. was found at Franklin, New Jersey by Dunn et al. (1982).

Orthorhombic, Jerrygibbsite

Its ideal composition

is close to that of sonolite

p. 243], and its cell dimensions humite mineral with c.

Jg

=

series

2(c sin a)

so

-- transformed

are related •

consists

so, it is the first such polymorph to be recognized;

White

their designation Winter

to those of sonolite

and Hyde

sonclite

(1982b) did not report

family

than the humite

If

families

it in their HRTEM 10, p. 267), but or (3,26,3).

would be (3,2,2,2,2,2,2,3)

et al. (1983) suggest that jerrygibbsite

Dunn et

sonolite".

or leucophoenicite

(see their Fig. 3 and Chapter

of this structure

the leucophoenicite

[Table 2, p. 234]

of "unit-ceil-twinned

in the humite

10,

to those of the

By analogy with ortho- and clino-pyroxene,

al. suggest that its structure

studies of Franklin

[see Table 4 in Chapter

to correspond

is more likely a member

of

family.

Dunn, P.J., D.R. Peacor, W.B. Simmons, Jr. and E.J. Essene (1982) Jerrygibbsite, a new polymorph of sonolite and member of the humite-leucophoenicite groups, from Franklin, New Jersey. Am. Mineral. 67, in press. Winter, G.A., E.J. Essene and D.R. Peacor (1983) Mn-humites from Bald Knob, North Carolina: mineralogy and phase equilibria. Am. Mineral. 68, in press .

• KANONAITE,

Mn3+A1SiO

S

e KASOLITE.

eKIMZEYITE,

See section

eKNORRINGITE,

of andalusite;

on URANYL SILICATES,

Ca3(Zr,Ti)2(Ai,Fe,Si)30l2'

eKIRSCHSTEINITE,

eKNEBELITE,

The Mn-analog

CaFeSi0 . 4

(Mn,Fe)Si0 • 4 Mg3Cr2Si30l2'

this chapter.

A garnet;

An olivine;

An olivine;

400

see Chapter

see Chapter

see Chapter

A garnet;

see Chapter

see Chapter

11.

11.

2.

2.

8.

e LAIHUNITE,

Fe

3+ 2+ F~O. 5 SiO4 .

Monoclinic Z

=

4.805, b

(subcell), P2llb; a

iO.187, c

=

91. 00;

S.80lA; S

4. Laihunite

ferrosilite, by Wang ity.

occurs in high-grade

almandite

and quartz.

metamorphic Conditions

(1980) to have been 600-700°C,

The rarity of these conditions The chemical

>15 kbar at relatively

accounts

more careful examination

Satellite

olivine~type reflections

vacancies

in x-ray and electron

refinement

diffraction

one with c'

of the latter indicated

on the Ml octahedral

High resolution

Sinica in 1976, but a

site is responsible

transmission

that laihunite has a

whose subcell has the dimensions

there are two sorts of superstructures, A least-squares

high oxygen fugac-

is Fei~00Fe~~S8MgO.08SiO.9604'

at Academica

by Shen et al. (1982) disclosed structure,"

fayalite,

were determine(

for the rarity of the mineral.

formula of the natural material

Its crystal structure was first determined

"distorted

rocks with magnetite, of crystallization

patterns

listed abov,

indicate

that

= 2c and one with c" = 3c. 2 that ordering of Fe + and for the superstructure.

electron microscopy

formed by oxidation

of fayalite.

cipitated magnetite

and a finely dispersed amorphous

showed laihunite

It commonly contains

to have

100-200A lamellae of pre-

phase.

Academica Sinica (1976) The crystal structure of laihunite. Hsuehi 1976, 104-106. Chem. Abstr. 85, 115090.

Ti Chi'iu Hua

Shen, B., O. Tamada M. Kitamura, and N. Morimoto (1982) Superstructure of laihunite (Fe6~5Fet~osi04): a nonstoichiometric olivine. I.M.A. Abstr.,

381.

Wang, Sheng-Yuan (1980) Thermodynamic analysis of the stability of laihunite. Ti Chi'iu Hua Hsuehi 1980, 31-42. Chem. Abstr. 93. 50757. Added in proof: Academica Sinica (1982) Laihunite -- a new iron silicate mineral. Geochemistry 1, 105-114. Ptngqiu, Fu, Kong Youhua and Zhang Liu (1982) Domain twinning of laihunite and refinement of its crystal structure. Geochemistry 1, 115-133. eLARNITE,

S-Ca Si0 . 2 4

Monoclinic, Larnite

P2l/n;

a = 5.502, b = 6.745, c = 9.297 A; S = 94.590;

occurs in calcsilicate

ture, low-pressure

rocks which have experienced

contact metamorphism.

Z = 4.

high-tempera-

It is also a phase in Portland

and slags and is important because of its hydraulic

activity,

cement

i.e., its ability

to harden when immersed in water. The structure

of larnite was determined

by Midgley

(1952) and corrected

and refined by Jost et al. (1977); it contains isolated

Si0 tetrahedra and 4 (see figure). The CaO 7 8 x are most densely packed in columns parallel to b, sharing triangular

3-dimensionally polyhedra faces.

connected Ca0

and Ca0

The columns are cross-linked

polyhedra

by sharing edges and corners. 401

.LARNITE,

continued

a

b

o (a) Column-like structural unit in larnite made up of CaO polyhedra. Common faces are hatched. (b) The S-Ca2Si04 structure, projectea along the y-axis. Large circle: Ca; +: Si; oxygens are at the corners of tetrahedra. From Jost et al. (1977, Figs. 3 and 2, respectively). Jost, K.H .. B. Ziemer and R. Seydel (1977) Redetermination of the structure of S-dicalcium silicate. Acta Crystallogr. B33, 1696-1700. Midgley, C.M. (1952) The crystal structure Crystallogr. 5, 307-312 .

• LEUCOPHOENICITE.

[Cell dimensions

and space group transformed

occurs

and as granular masses

-- see Chapter "as crystals

with green willemite,

franklinite"

from Moore

tephroite,

cf.

leucophoenicite

glaucochroite Palache,

and Moore

multiple

cell which he later found to be a pseudo-cell

superficially

leucophoenicite. related

an "O-leucophoenicite"

formula Mn7[Si0412[(Si04)(OH)21. on hcp oxygens stacked parallel

of the structure

402

cry-

and not allied to the with an orthorhombic

built of multiply-twinare at least

(see Table 1 in Ch. 10, p. 234). yielded

As with the humites, to (100).

and coarsely

1935).

In fact the lattice parameters

to those of the Mn-humites

(1970) determination

veins

... usually

was thought to be the Mn-iso-

humites,

But Moore's

New Jersey,

(1935) found it to be monoclinic

(1967) reported

to

10.1

(Moore, 1970, p. 1146;

Pal ache

;

(1970) to conform

in late state open hydrothermal

in ore and skarn from Franklin,

Because of its composition,

ned monoclinic

Z = 2.

0

Leucophoenicite

type of humite.

Acta

P2llb; a = 4.826, b = 10.842, c = 11.324 A; a = 103.93

those of the humite minerals

stalline

silicate.

3Mn Si0 ·Mn(OH)2' 2 4

Monoclinic,

in association

of S dicalcium

the crystallochemical

its structure

"The octahedral

populations

is based define

.LEUCOPHOENICITE,

continued

a new kind of kinked plaining

serrated

the frequent

"The octahedrally populations.

tetrahedra:

populated

age composition

tetrahedral

SiO(7)terminal

Si-0(4)basal

=

1.794

A,

both

electrostatic

by three octahedral 2+

albeit

(1972a,b)

stereochemistry

Thus leucophoenicite

structures

twinning

observed hedral

to be coherently

intergrown.

diffraction

c-axis,

patterns"

structure

orthorhombic

Like Moore reflections

of ordering

but rejected

for which there was no evidence

403

in

to rationalize

of the leucophoenicite

was considered

Figures a and b are on the next page.

(figure b)

on a unit cell scale was observed

"The possibility

(White, 1982, p. 92).

by three an ortho-

et al., 1974.]

twins that would be required

faulted members

Si) in the [100] direction

result in a doubled

is coordinated

(Fig. 14, Ch. 10).

patterns";

polysynthetic

in a locally

is technically

the leucophoenicite

X-ray powder

Various

with the unoc-

results

[See also Belokoneva

"additional

those reflections.

when the Si(l) atom

one.

to explain

but not the periodic

an octa-

in which each oxygen is coordinated

(1970), they were unable diffraction

where terminal

the OH ions are associated

describe

in the same terms as the humite

and Si-O(S)\asal

in such a shared edge (see figure a).

charge distribution

a most unusual

where 0(7) ...0(7')

in an edge shared between

Mn2+ plus one Si4+ and each hydroxyl

White and Hyde

A,

Si(l) tetrahedra,

[O.SSi = (OH)0.SOo.5)'

This unusual

, just as in the Mn-humites.

silicate,

quite unique for

= 1.764

only to oxygens because,

say the left tetrahedron,

cupied right tetrahedron. neutral

pairs, with the mid-

This pair has an aver-

and basal refers to a bond to any oxygen or

O,OH anion that is involved

Both Si(l) and Si(2) are bonded occupies,

I.

group are therefore Si-0(7')basal

the half-occupied

hedron and the Si(l) tetrahedron

Mn

A,

= 1.519

to the bond to an oxygen not involved

disordered

tetrahedral

point symmetry

tetrahedra

half-occupied

[(Si0 )(OH)2] and its presence results in unusual but explic4 distortions" (Moore, 1970, p. 1146). Bond lengths in the centro-

is the edge shared between

A,

on the tetrahedral

there is a set of fully occupied

edge possessing

[Si(1)04(OH)216-

silicates:

to the z-axis, ex(see the figures).

chains place restrictions

these latter occur as edge-sharing

able polyhedral

1.771

on {001}"

1 [Si(2) in figure a) and a set of disordered

point of the common

refers

... running parallel

by reflection

For leucophoenicite,

with point symmetry

symmetric

chain

twinning

family were [of tetra-

because

it would

in X-ray or electron

• LEUCOPHOENICITE,

continued

a (a) Polyhedral diagram of the structure of of edge-sharing octahedra (shaded) and the sharing Si(l) tetrahedra which are related between the 0(7) oxygens with (OH).50.5 at hedron is similar to those in the humites.

leucophoenicite, showing one chain unique pair of half-occupied edgeby a center of symmetry half-way 0(4) and 0(5). The Si(2) tetraFrom Moore (1970).

(b) In the upper portion of this figure the leucophoenicite structure is represented as an anion-stuffed ccp array of cations (see Chapter 10, p. 6 for full discussion). Half of the face-sharing Mn6 trigonal prisms (those outlined with dashed lines) are occupied by Si in a statistical manner. The "twin formula" is (1,23). From White (1982, Fig. 1.12, p , 17). Belokoneva; E.L., M.A. Simonov and N.V. Belov (1974) Structures of leucophoenicite, Mn7[Si04]2[(Si04)(OH)2], and synthetic Cd orthogermanate, Cd3[Ge04] (OH)2' Sov. Phys. Crystallogr. 18, 800-801. Moore, P.B. (1967) On leucophoenicites: Mineral 52, 1226-1232.

I. A note on form developments.

(1970) Edge-sharing silicate tetrahedra -----phoenicite. Am. Mineral 55, 1146-1166.

in the crystal structure

Am. on leuco-

Palache, C. (1935) The minerals of Franklin and Sterling Hill, Sussex County, New Jersey. U.S. Geo1. Surv. Prof. Paper 180, 104-105. T.J. (1982) An Electron Microscope Study of the Humite and Leucophoenicite Structural Families. Ph.D. dissertation, Australian National Univ.,

White,

Canberra. and B.G. Hyde (1982a) A description of the leucophoenicite family of structures and its relation to the humite family. Acta Crystallogr., in press. and (1982b) -----Miner~submitted)

• LIEBENBERGITE,

• LUSAKITE.

Ni Si0 . 2 4

A cobaltan

An electron microscope .

An olivine;

staurolite;

study of leucophoenicite.

see Chapter

see Chapter

404

7.

11 .

Am.

.MAJORITE,

Mg3(Fe,Si,Al)2Si30l2'

Cubic, Ia3d. Majorite thene.

a = 11.524 A; Z = 8.

is garnet occurring in meteorites

It presumably

of a pyroxene

with a composition

forms as a result of extraterrestrial

(Smith and Mason, 1970; Coleman, 1977).

Coleman, L.C. (1977) Ringwoodite and majorite Canadian Mineral. 15, 97-101.

CaSnSiOS'

• MANGANHUMITE,

shock metamorphism

See also Chapter 2.

in the Catherwood meteorite.

Smith, J.V. and B. Mason (1970) Pyroxene-garnet meteorite. Science 168, 832-833 .

• MALAYAITE,

near hypers-

transformation

in the Coorara

The tin analog of titanite; see Chapter S .

3Mn2Si04'Mn(OH)2'

The Mn-analog

of humite; see Chapter 10.

Hexagonal. Melanocerite

occurs in nepheline-syenite

pegmatites

way and at Wilkerforce,

Ontario.

but with less thorium.

It is mostly metamict,

the Wilkerforce 1970).

material

of Langesundfiord,

It may be the same mineral

but single-crystal

x-ray work on

suggests that it may have the apatite structure

See the section on SILICATE

APATITES>

Nor-

as tritomite,

(Erd,

this chapter.

Erd, R.C. (1970) Monthly project report, listed under "Melanocerite". In M. Fleischer (1981) The Ford-Fleischer File of Mineralogical References. U.S.G.S. Open-File Report 81-1169 .

• MERWINITE,

Ca Mg[Si0 1 . 3 4 2

Monoclinic Merwinite

P211a; a = 13.254, b = 5.293, c = 9.328 A; S = 91.90

0

;

Z = 4.

is a major component of silicate slags used in the manufacture

of iron, steel and cement, and it is of particular value industrially

because,

unlike Ca2Si04, it does not go through polymorphic transformations when it is cycled from low to high temperatures. In nature, merwinite is found only in skarns; it was first described by Larsen and Foshag at Crestmore, gehlenite,

California.

occasionally

It is invariably

with monticellite

"Where diopside and wollastonite winite was observed Divalent

± spinel, and rarely with

are abundantly

to be rare or absent"

Fe and Mn may substitute

for Mg. 405

(1921) as a major constituent

associated with spurrite and idocrase.

associated with gehlenite, mer-

(Moore and Araki, 1972, p. 1356).

• MERWINITE,

continued

The stability

of merwinite

ceramic and steel industries,

in the system CaO-MgO-Si0 , so important to the 2 on the ternary phase equilibrium

is represented

diagram compiled by Osborn and Muan ibria of the assemblages

(1960).

Walter

found at Crestmore,

(1965) evaluated

California.

the equil-

Franz and Wyllie

at 1 kbar in the system CaO-MgO-Si0 2 (1964) found that the assemblage merwinite +

CO -H ), and Kushiro and Yoder 2 2 forsterite s.s. + diopside persists up to at least 38 kbar at lSOO°C. (1968) concluded

(1967)

is stable above 75SoC

found that merwinite

that merwinite

regions of the upper mantle.

may be an important mineral

Moore and Araki

(1972) remarked

with a volume per anion of 20.6 A3 and density 3.32 glcc,

Yoder

in Ca-rich,

Si-poor

that merwinite,

is 10% more dense

than its "olivine" counterparts, a-larnite (3Ca Si0 ) + forsterite (Mg Si0 ), 2 4 2 4 and that its high coordination numbers for Ca (8 and 9) and density are 2 achieved by having both 02- and Ca + mixed together in the "dense-packed" layers, somewhat

like the hollandite

The structure

of merwinite

and perovskite

structures.

was solved by Moore and Araki

(1972 -- henceforth

M & A), who first had to sort through much chemical and crystallographic formation.

A projection

and edge-sharing

linkages amongst the Si0

the three irregular

CaOS and Ca0

layers, each consisting

along the a-axis. 4

of

synthetic

tetrahedra, the Mg0 octahedra and 4 6 polyhedra. The three types of dense-packed

9 of 2 Ca + 4 oxygen atoms, are variously

A, B, and P, and the stacking

hedra and Si0

misin-

down the [0101 (figure a) shows some of the corner-

Figure b is a polyhedral

tetrahedra

rnerwinite

are

in a "pinwheel" a

The ranges of values observed

indicated

as

sequence is ...ABPABP ... for a total of six layers

1.706, S

diagram of a (100) slab of Mg0

arrangement.

=

1.711-12,

in merwinite

octa6 indices

The refractive

y

from blast furnace slags and in

nature are a = 1.705 - 1.710, S = 1.711 - 1.714, Y = 1.718 - 1.728; 2Vy = 67-750 (Phemister, et al. 1942). {OlO} (Tilley, 1929). and represents

It is the {lOO} cleavage

a direction

[0111) prisms are predominant

Hardness

Morphologically,

face being

in natural

A), not

[0111 (or

but pseudo-trigonal

plane {110) are rel-

specimens and a less common set has twin plane and

plane {lOO} (Larsen and Foshag, 1921).

See discussion

&

{lOO} are often observed.

twins with twin axis [0011 and composition

common

composition

is 6.

in synthetic merwinite,

tabular crystals with the most prominent

atively

(M

slabs (figure b)

in which only the weak Ca-O and not the stronger

Mg-O or Si-O bonds need be broken.

Polysynthetic

that is "good"

This is the plane of the dense-packed

f:iREDIGITE> Ca'V3.SMg'V0.S[Si0412' this chapter.

Figures a and b are on the next page.

406

• MERWINITE, A Mg B Si

continued P

Si A

Mg B Si

P Si A

A B Co(2)+Co(3)+0(1)+0(2)+0(3)+0(5)+0(7)+0(8)

Mg

0

0

p , 2Co(I)+2 0(4)+20(6)

~ ~ ~~ ~ ~~ ~ ~~ t ~t t

Mg

0

s:

°5i(I)+5i(2)

2Mg

a (a) Spoke diagram of the merwinite structure projected down the b-axis. The Si0 4 and Mg06 slabs are shown at a'v 0, ~ and these slabs are parallel to {lOO}. The Ca-O bonds are dashed. Locations of the A- and B-dense-packed layers, the P-layer, and the Mg and Si atoms along the a-axis are indicated above. Heights at atoms are in fractional coordinates along the y-direction. After Moore and Araki (1972, Fig. 3, p. 1364). (b) Polyhedral diagram of a slab of Mg06 octahedra and Si04 tetrahedra down the x*-axis. Note the pseudo-hexagonal character of the "pinwheel" arrangement. After Moore and Araki (1972, Fig. 5, p. 1366). Franz, G.W. and P.J. Wyllie (1967) Experimental studies in the system CaO-MgOSi0 -C0 -H 0. In P.J. Wyllie, ed., Ultramafic and Related Rocks> John Wiley 2 2 2 & Sons, New York, p. 323-326. Kushiro, I. and H.S. Yoder, Jr. (1964) Breakdown of monticellite and akermanite at high pressures. Carnegie Inst. Washington Geophys. Lab. Reo, 1963-1964, Sl-S3. Larsen, E.S. and W.F. Foshag (1921) Merwinite, a new calcium magnesium silicate from Crestmore, California. Am. Mineral. 6, l43-l4S.

ortho-

Moore, P.B. and T. Araki (1972) Atomic arrangement of merwinite, Ca3Mg[Si04]2' an unusual dense-packed structure of geophysical interest. Am. Mineral. 57, 1355-1374. Phemister, J., R.W. Nurse, and F.A. Bannister mineral. Mineral. Mag. 26, 225-231.

(1942)

Merwinite

as an artificial

Tilley, C.E. (1929) On larnite (calcium orthosilicate, a new mineral) and its associated minerals from the limestone contact zone of Scawt Hill, Co. Antrim. Mineral. Mag. 22, 77-S6. Walter, L.S. (1965) Experimental studies on Bowen's decarbonation series III: P-T univariant equilibrium of the reaction: spurrite + monticellite ~ merwinite + calcite and analysis of assemblages found at Crestmore, California. Am. J. Sci. 263, 64-77. Yoder, H.S., Jr. (196S) Akermanite and related melilite-bearing assemblages. Carnegie Inst. Washington, Geophys. Lab. Report 1966-1967, 471-474. 407

• MONTICELLITE,

CaMgSi0 . 4

• NA BOLTWOODITE

.

• NATISITE,

See section

• FERSMANITE,

y

,

P4/nmm; a

Pl or pI;

=

0

89.04

Natisite

=

Z

;

occurs

a

R;

z =

2.

from the nepheline-bearing

U.S.S.R

+ ussingite-bearing

An average

pegmatites

S

of four microprobe

The chemistry

to be a fluorine-bearing,

titanoniobosilicate

(1936) and Labuntsov

analyses

there have been a number

mas-

of natisite

is complex

gave

spectra

but was shown

of Na and Ca by BornemanIn absence

of formulae

is believed

of a structure

proposed.

(1977) who found the main substition

ceeds Nb and the charge balance

was de-

Khibiny

An infrared

of fersmanite

(1933).

of the Lovozero

Fersmanite

of the neighboring

of Nal.99(TiO.99MnO.01FeO.01NbO.Ol)Sil.010S'

is from Machin

95.150,

a

veinlets

et al., 1975).

(Men'shikov

showed no water present.

Starynkevich

A;

4.

in natrolite

1929).

= 5.107

b = 7.213, c = 20.451

= 7.210,

scribed

mination,

this chapter .

(F,OH)2'

Kola Peninsula,

sif (Labuntsov,

c

= 6.480,

massif,

a formula

11.

on URANYL SILICATES>

(Ca,Na)4(Ti,Nb)2Si20ll

Triclinic, 95.60

see Chapter

Na TiOSi0 . 2 4

Tetragonal,

0

An olivine;

deter-

The one given above

is CaTi = NaNb.

to be maintained

Na ex-

by the replace-

ment of some oxygen by hydroxyl. Natisite

and fersmanite

are the sodium analogues of titanite, CaTiOSi0 • 4 2 of Na+ for Ca + could be accomplished in several ways; among

The substitution them:

2Na+ = Ca2+ = Ca2+ + Ti4+

Na+ + (Nb,Ta)5+

Na+ + (OH,F)- = Ca2+ + 0(1)2The completion whereas

of the 2Na = Ca substitution

the Na(Nb,Ta) (OH,F) = CaTiO(l)

is the mineral

substitution

natisite, Na TiOSi0 , 2 4 leads to the mineral

fersmanite. The crystal

structure

of synthetic

al. (1964) and Nyman et al. (1978). tetrahedral atoms

sharing

(figure a).

corners The Ti0

one short Ti-O distance is comparable and B

=

P,S,Mo

with Ti0

5 polyhedron

natisite

was determined

The structure polyhedra

consists

alternating

is a square pyramid 5 and four longer ones. The general

to a group of tetragonal

(cf. Longo and Arnott,

AOB0

4 1970).

Figures a, b> and c are on the next page. 408

compounds

by Nikitin

et

of layers of Si0

4 with layers of Na (figure b) with structure

of natisite

where A = Ta,Nb,Mo

In these compounds

and V

the absence

.NATASITE

and FERSMANITE,

continued

No layer

b

f

c'5.107 A

0(2)

1

0(1)

;'-0=6.480

A~

(a) The structure of synthetic natasite, Na TiSiO ' projected onto 001. Large 2 S open circles are 0, large filled circles Na, small open circles Ti, and small filled circles Si. Elevations are in c/lOO. Square pyramids with apices pointing down have basal faces cross-hatched, the others point up. From Nyman et al. (1978, their Fig. 1). (b) Dimensions and geometry of the TiOS square pyramid in synthetic natisite, Na TiSiOs. Data is from the refinement of Nyman et al. 2 (1978). (c) The structure of Na TiSi0 viewed on 010 showing layers of Si0 2 5 4 tetrahedra and Ti0 square pyramids alternating with layers of Na atoms. Large 5 open circles are oxygen, large patterned circles Na and small filled circles Ti. Dotted lines show the imagined, distorted octahedral coordination of the Ti to produce the octahedral chains foun,1 in the tetragonal AOB0 compounds. 4

of Na between

the layers allows

the square pyramids

to distorted

corner-shared

octahedra

by tetrahedra

which

forming

the layers

to come closer

octahedra.

chains parallel

share the remaining

together,

The main structural

corners

to c.

converting

units are

The chains are coupled

of the octadra.

Figure

c shows

structure

of Na TiOSi0 drawn to show its similarity to the AOB0 compounds. 2 4 4 This would produce alternating short and extremely long Ti-O(l) bond distances parallel bond distances dination

toc : 1.695 and 3.412 A compared of 1.990

in natisite,

in that they alternate The titanite

(see Chapter

While clearly

the A-O(l)

Ti0

bond distances

is also comparable octahedra

6 5, this volume).

to the equatorial

in AOB0

compounds

4 to the c axis.

to that of natsite,

which are cross-linked

However, 409

Ti-0(2)

the Ti is not in octahedral

long and short parallel

structure

chains of corner-shared hedra

A.

the octahedral

coor-

are similar

containing

by Si0

tetra4 chains in titanite

.NATASITE

and FERSMANITE,

are kinked. a four-fold AOB0

If they are straightened symmetry

axis parallel

Substitution

compounds.

4 produce natisite. substitution

continued and the Ca omitted,

titanite would gain

to the chains and be isostructural

with the

of Na in the channels between

These structural

modifications

required

the chains would 2 by the 2Na+ ~ Ca +

limits the solid solution of titanite and natisite.

The alternating

long-short

bond distances

of the octahedral

chains paral-

lel to c in the AOB0 also has a perfect

compounds results in a perfect 001 cleavage. Natisite 4 001 cleavage, the Na atoms only weakly bonding the Si04 +

Ti0 layers. The off-center displacement of the A-site cations (Ti,Nb,Ta,Mo, 5 V) in an octahedron is characteristic of oxygen-octahedral ferroelectrics. The antiparallel

displacements

of the cations

in adjacent

chains in the AOB04 comthat these are antiferroelectric.

pounds and titanite has lead to the suggestion While

the Ti octahedron

similarities,

in natisite

the Ti is off-centered

lel displacement

in adjacent

be antiferroelectric

is a contrivance

for showing structural

in the TiO

coordination

square pyramid. The antiparalS polyhedra would suggest that it may

as well.

Borneman-Starynkevich, I.D. (1936): Composition of several titanosilicates from the Khibiny tundras. Vernadsky Jubilee Volume, Akad. Nauk SSSR 2, 735-755. Laruntsov, A.N. (1929) Fersmanite, a new mineral Akad. Nauk, Leningrad, Ser. A, 12, 297-301.

(1933)

Mineralogical

of the Khibiny Massif.

Dokl.

Survey of the Central Part of the Khibiny Massif

(Deposits of Zircon, Catapleiite 202-208, Leningrad, Khimteoret.

and Fersmanite).

Longo, J.M. and R.J. Arnott (1970) Structure J. Solid State Chem. 1, 394-398. Machin, M.P. (1977) Fersmanite ian Mineral. 15, 87-91.

Khibinsky

and magnetic

(Ca,Na)4(Ti,Nb)2Si20ll

apatity,

properties

(F,OH) : 2

6,

of VOS04·

a restudy.

Canad-

Men'shikov, Yu , P., Ya. A. Pakhomovskii, E.A. Goiko, LV. Bussen and A.N. Her' kov 1975. A natural tetragonal titanosilicate of sodium, natisite. Zapiski Vses. Mineralog. Obshch. 104, 314-317. Am. Min. 61, 339. Nikitin, A.V., Ilyukhin, V.V., Litvin, B.N., Kel'nikov, O.K. and Belov, N.V. (1964) Crystal structure of the synthetic sodium titanosilicate, Na2TiOSi04• Dokl. Adad. Nauk SSSR 157, 1355-1356. Nyman, H., O'Keefe, M and Bovin, J.O. (1978) Acta Crystallogr. B34, 905-906.

410

Sodium

titanium

silicate,

Na2TiSiOS'

.NELTNERITE,

CaMn Si0 . 6 12

I4llaed; a = 9.464; c = 18.854 !; Z = 8.

Tetragonal, Neltnerite at Techgagalt, Fe as well braunite,

is part of a vein assemblage Anti-Atlas

Mtns., Morocco.

et al., 1982).

(Baudracco-Gritti the Ca occupying

See BRAUNITE,

the distorted

with Mn- and Ca- bearing minerals

The mineral

contains

Neltnerite

Mn(l) cube site

a small amount of

is isostructural

with

(Damon et al.> 1966).

this chapter.

Baudracco-Gritti, C., R. Caye, F. Permingeat, and J. Protas (1982) La neltnerite CaMn6Si012 une nouvelle espece minerale du groupe de la braunite. Bull. Mineral. 105, 161-165. Damon, J.L., F. Permingeat and J. Protas (1966) Etude structurale CaMn6Si012• C.R. Acad. Sc. Paris, 262, Ser. C. 1671-1674 . • NORBERGITE,

Mg2Si04·MgF . 2

A humite mineral;

see Chapter

du compos~

10.

The manganese analog of chloritoid; see Chapter 6 . • PARASPURRITE,

CaS(Si04)2C03'

Monoclinic, Paraspurrite

occurs

ed at high temperatures chemistry

=

P21la ; a

in calcsilicate

6.705, c

=

principally

Colville

in a roof pendant

=

90.580;

Z = 8.

in a syenite.

Paraspurrite

by having a doubled

and Colville

(see figure) based on that of spurrite

27.78 A; S

rocks that have been contact-metamorphos-

that of the ideal formula.

differing

in the c* direction.

=

and low pressures

is essentially

morph of spurrite

10.473, b

unit cell dimension

(1977) have proposed

by Kletsova

and Belov

Its

is a poly-

a structure

(1961).

Proposed structure for paraspurrite projected onto (010) based on diagram of Kletsova and Belov (1961). The monoclinic unit cell of spurrite is outlined by dashed lines for comparison. Shaded triangles are C03 groups; si0 tetra4 hedra are labelled 25 and 75 to indicate fractional coordinates along b; the other polyhedra contain Ca.

.'PARASPURRITE,

continued

Colville, A.A. and P.A. Colville (1977) Paraspurrite, a new polymorph of spurrite from Inyo County, California. Am. Mineral. 62, 1003-1005. Kletsova, R.F. and N.V. Belov (1961) Crystal Physics - Crystallogr. 5, 659-667 •

• PICROTEPHROITE,

• RINGWOODITE,

(Mg,Mn)Si0 . 4

A high-pressure has practically

traterrestial

8.l-8.2A; polymorph

collision.

Soviet

11 .

=

8.

of olivine, ringwoodite as the coexisting

occurs in meteorites olivine.

from olivine by shock transformation Analysed

ringwoodites

and refractive

ported by Ringwood +

resulting

have compositions

is the spinel or y form of (Mg,Fe)2Si04' index of the synthetic

and Major

ringwoodite

(1968) and Ringwood

material

(1966, see the figure). transition and Major

is

from ex-

of approximately 1977).

Variation

of cell

with composition

is re-

The P-T-X phase relations

have been studied by Akimoto (1970).

and

Ringwoodite

(Binns et al., 1969; Mason et al., 1968; Coleman

Ringwoodite

of the olivine

Z

the same composition

(Mg.75Fe.25)2Si04

Fujisawa

=

to be produced

dimension

see Chapter

of spurrite.

(Mg,Fe)2Si04'

Cubic, Fd3m; a

thought

An olivine;

structure

At compositions

and

more magnesian

than F080 orthorhombic S-(Mg,Fe)2Si04' rather than ringwoodite, is the high pressure polymorph (Ringwood and Major, 1970). See Chapter 11, pp. 353-355 for further discussion. The crystal

structures

have been reported

of synthetic

disordered.

"ringwoodites"

by Sasaki et al. (1982) and Marumo et al. (1977).

space group Fd3m, and the crystal

Ringwoodite

Mg- and Fe-end-member

parameters

They have

are

y-Mg Si0 a = 8.065A, µ = 0.3685 2 4 y-Fe Si0 a = 8.234A, µ = 0.3659 2 4 has a normal spinel structure; the synthetic analogs are partially Site occupancies

sites and 90-99%

are estimated

(Mg,Fe) in the octahedral

to be 80-98% Si in the tetrahedral sites. n

Variation in refractive index (n) and cell dimension (a) with composition in synthetic (Mg,Fe)2Si04 spinels. (after Binns et al., 1969) 412

s.o

O':-~-:2'-:O~----:4':-O~--:6':-O~--:8':-O~_J,OO mo I percent

• RINGWOODITE,

continued

Akimoto, S. and H. Fujisawa (1968) Olivine - spinel solid solution equilibria in the system Mg2Si0 - Fe Si0 . J. Geophys. Res. 73, 1467-1479. 4 2 4 Binns, R.A., R.J. Davis and S.J.B. Reed (1969) Ringwoodite, natural (Mg,Fe)2Si04 spinel in the Tenham meteorite. Nature 221, 943-944. Coleman, L.C. (1977) Ringwoodite and majorite Canadian Mineral. 15, 97-101.

in the Catherwood meteorite.

Marumo, F., M. Isobe and S.Akimoto (1977) Electron-density distributions in crystals of y-Fe2Si0 and y-Co Si0 . Acta Crystallogr. B33, 713-316. 4 2 4 Mason, B., J. Nelen, J.S. White, Jr. (1968) Olivine - garnet transformation in a meteorite. Science 160, 66-67. Ringwood, A.E. and A. Major (1966) Synthesis of Mg2Si04-Fe2Si04 solutions. Earth Planet Sci. Letters 1, 241-245.

spinel solid

Ringwood, A.E. and A. Major (1970) The system Mg2Si04-Fe2Si04 at high pressures and temperatures. Phys. Earth Planet. Interiors 3, 89-108. Sasaki, S., C.T. Prewitt, Y Sato and E. Ito (1982) Single-crystal of Y-Mg Si0 . J. Geophys. Res. 87, 7829-7832. 2 4

eSCHORLOMITE,

Ca3(Fe,Ti)2(Si,Fe)30l2'

x-ray study

A garnet; see Chapter 2.

e SILICATE APATITES

ELLESTADITES Apatite adaptable

and BRITHOLITES

is a calcium phosphate,

to numerous chemical

CalO(P0 )6(OH,F,Cl)2' whose structure is 4 substitutions. Hith reference to the general

formula A10(X04)6Z2' silicate apatites are found to be of two major types: (1) the britholites

with A = REE and X

=

Si, and (2) the ellestadites

with A

Ca and X = Si and S.

primarily

The structure of apatite was refined by Beevers

(1946).

The isolated

T04 groups are bound together by large A cations in irregular coordination (see figure). calciums

Monovalent

Z anions "just fit into a triangle of three

[or A cations] on each mirror plane intersecting

lel to c at the corners of the hexagonal monoclinic distortions

unit cell.

symmetry are strongly pseudohexagonal of the structure

to accommodate

X and 7, sites.

Figure is on the next page. 413

the channel" paral-

Silicate apatites with

and would require slight

the variety of atoms at the A,

• SILICATE APATITES,

continued

structure

Ellestadites,

the Silicate-Sulfate

McConnell

is maintained

CaS(P04)3F. lines. bond(1965,

Apatites

(1937, 1938) first suggested

apatites with the isomorphous

of aparite,

substitution

that charge balance

in phosphate

of Si but lacking rare-earth

elements

by the substitution Si+4 + S+6 ~ 2P+S

This was based on the chemistry known, wilkeite More recently, sentially

of the two silicate-bearing

(Eakle and Rogers,

1914) and ellestadite

Rouse and Dunn (1982) have shown that the ratio

1:1 for a range of compositions

Crestmore,

California.

termed ellestadites.

lestadite)

and Z

of silicate-sulfate

They also proposed Designations

of three possible

=

Cl (chlorellestadite).

in some apatite analyses

ing from the additional

then 1937).

of S:Si is esapatites

that apatites with ~(Si,S) end-members

Deviation

is explained

of Ca

from >

P be (Si04)3

lO Z = F (fluorel-

those with Z = OH (hydroxyle1lestadite),

(S04)3 Z 2 include

1:1 observed

apatites

(McConnell,

of the Si:S ratio from

by Vasileva

(1958) as result-

coupled substitutions

3P+S + 0-2 ~ S+6 + 2Si+4 + OH- or Ca+2 + p+S ~ Na+l + S+6. Synthetic Takemoto

OH, F and Cl ellestadites and Kato

(1968) and Pliego-Cuervo

Ellestadites lestadites

have been reported

are normally

from the Chichibu Mine,

with both hexagonal

and Glasser

thought to be hexagonal. Saitama Prefecture,

by Dihn and Klement

(1942),

(1978). However, hydroxylelJapan have been reported

(Harada et al.> 1971) and monoclinic

symmetry

(Sudarsanan,

6.92 A. space group is P6 1m or P6 with a = 9.49, c 3 3 The monoclinic space group is reported as either P2 /m or P2 with a = 9.476, l l b = 9.508, c = 6.919 A and y = 119.530• This is not a standard setting for mono1980).

The hexagonal

clinic apatites; [Note:

the hexagonal

to monoclinic

The space group of monoclinic

transformRtion

Cl-apatite

is r2 1a. 1

matrix

is 200/001/010.

• SILICATE

APATITES,

Sudarsanan

continued

(1980) reported

lestadite

from the Chichibu

resembles

apatite.

on the crystal

(Si,S)-O

distances

of Si and S on the different

A

Si - 0 = 1.62

associated

careous

Sand

indicate

incomplete

sites; the mean bond length of

A

(Wuensch,

1972).

Sudarsanan

OH,the other with Cl.

Si are reported

as trace constituents

Si- and S-rich phosphate

(McConnell,

by coupled

apatites

in apatites

Silicate

from a variety

and ellestadites

high-temperature,

low-pressure

1937; Harada et al.> 1971; Vasileva,

Rare-earth

Charge balance structure

The structure

sites with average

These distances

tetrahedral

(Liebau, 1972) and S - 0 = 1.47

rocks which have undergone

Britholites,

tetrahedral

two groups of sites for the Ca(2A,B,C) atoms; one group is

of occurrences,

morphism

A.

of 1.52, 1.54 and 1.57

with For

While

of natural hydroxyel-

l

There are three differing

ordering

also reports

structure

Mine refined in the space group P2 la.

occur in calcontact meta-

1958).

Apatites

can be maintained

with P ~ Si substitution

in an apatite

substitution of a trivalent cation in the A site: 3Si+4 + 3(REE,y)+3 + 2Ca+2 ~ 3P+5 + SCa+2.

This leads to the formula

which represents silicate

called britholite-Y.

but incompletely Vlasov

(REE'Y)3 Ca2 (Si04)3 (OH,F,Cl), called britholites and the yttrium-REE

the REE silicates,

described

There are a number

substances

(1966), Ito (1968) or Gay (1957).

have been synthesized Mn and Cd (Cockbain plete solid solution as only an incomplete

of varietal

which are discussed

Many of the REE end-member

as well as bri tholi tes with Ca replaced and Smith, 1967; Ito, 1968; Sheyakov between

apatite

solid solution

names for related,

and referenced

and britholite-Y exists between

in

britholites

by Mg, Sr, Ba, Pb,

et al., 1972).

A com-

has been synthesized, apatite

where-

and britholite-La

(Ito, 1968). A number

of alkali-

been synthesized

and alkaline-

rare earth silicate-phosphate

and crystallographically

characterized.

apatites

Fedorov et al. (1975)

REE6

(S104)4

REE6

(Si04)6

Cockbain

(1968)

REES

(Si04)6

Cockbain

(1968)

REE4

(Si04)6 (Si04) 3

Cockbain

(1968)

REE4.67

have

These include

o

(Li,Na,K)

Kuz'min & Belov (1966) Belokoneva et al. (1972) Felsche (1973); Ito (1968) Pushcharovskii et al. (1978) Cockbain & Smith Ito (1968)

415

(1967),

• SILICATE APATITES, These compounds or halogen

continued

are of interest

site elements

because

in analyses

with one of these possible

of britholites

apatite.

However,

with

the synthetic vestigate

occurs

entiation

in the Shonkin

solid solution

in apatites

space group P63/m

as optically although

Cockbain

distributions

in carbonatites

enrichment

britholites

above.

of the A cations

the distribution

Britholite

of a britholite,

mentioned

La were found to have random

described

of cations

or P63

that they are isostructural

are often described

refinement

oxyapatites

may represent

are hexagonal,

the interpretation

britholites

has been no structure

that deficiencies

end-members.

Gay (1957) found that britholites which is consistent

they suggest

biaxial.

There

there are several

and Smith

in a synthetic

with

britholite-La:

Ca and

over the 4f and 6h sites.

and alkaline

igneous

rocks.

Nash

(1972)

of Si, Na, K, Sr and REE with increasing

Sag laccolith,

for

(1967) did in-

Montana;

with extreme

differ-

differentiation

were found in the soda syenites.

Belokoneva, E.L., T.L. Petrova, M.A. Simonov and N.V. Belov (1972) Crystal structure of synthetic TR analogs of apatite DY4 67[Ge04)30 and Ce4 67[Si04)30. Sov. Phys. Crystallogr. 17, 429-431.' . Cockbain, A.G. 654-660.

(1968)

The crystal

chemistry

of the apatites.

Cockbain, A.G. and G.V. Smith (1967) Alkaline-earth apatites. Mineral. Mag. 36, 411-421. Dihn, P. and R. Klement Chem. 48, 331-333.

(1942)

Isomorphe

Mineral.

rare-earth

Apatitarten.

Mag. 36,

silicate

Z. Electrochem.

germanate

Ang. Phys.

Eakle, A.S. and A.F. Rogers (1914) Wilkeite, a new mineral of the apatite group, and okenite, its alteration product, from Southern California. Am. J. Sci., 4th Ser. 37, 262-267. Fedorov, N.F., I.F. Andreev and N.S. Meliksetyan (1975) Growth and study of single crystals of alkali earth and rare earth oxysilicates phosphate apatites. Sov. Phys. Crystallogr. 20, 280-281. Felsche, J. (1973) The crystal and Bonding 13, 99-197.

chemistry

of the rare-earth

silicates.

Structure

Gay, P. (1957) An x-ray investigation of some rare-earth silicates: cerite, lessingite, beckelite, britholite and stillwellite. Mineral Mag. 31, 455-468. Harada, K., K. Nagashima, K. Nakao and A. Kato (1971) Hydroxylellestadite, a new apatite from Chichibu mine, Saitama Prefecture, Japan. Am. Mineral. 56, 1507-1518. Ito, J. (1968)

Silicate

apatites

and oxyapatites.

Am. Mineral.

Kuz'min, E.A. and N.V. Belov (1966) Crystal Structure of La and Sm. Sov. Phys. Dokl. 10, 1009-1011. Liebau,

F. (1972)

Silicon.

Handbook of Geochemistry,

53, 890-907.

of the simplest

l4-A CrYstal chemistry. In K.H. Wedepohl, Vol. II/2, p. l4Al-14A32.

silicates Ed.,

McConnell, D. (1937) The substitution of Si0 - and S04-groups for P04-groups in 4 the apatite structure; ellestadite, the end member. Am. Mineral. 22, 977-986. (1938) A structural investigation Am. Mineral 23, 1-19.

of the isomorphism

of the apatite

group.

eSILICATE

APATITES,

continued

Nash, W.P. (1972) Apatite chemistry and phosphorus igneous intrusion. Am. Mineral. 57, 877-886.

fugacity

~n a differentiated

Pliego-Cuervo, Y. and F.P. Glasser (1978) Phase relations and crystal chemistry of apatite and silicocarnotite solid solutions. Cement Concrete Res. 8, 519-524. Pushcharovskii, D. Yu., G.I. Dorokhova, E.A. Pobedimskaya and N.V. Belov (1978) Potassium-neodyium silicate KNd9(Si04)602 with apatite structure. Sov. Phys. Dokl. 23, 694-696. Rouse, R.C. and P.J. Dunn (1982) A contribution to the crystal chemistry of ellestadite and the silicate sulfate apatites. Am. Mineral. 67, 90-96. Shevylakov, A.M., I.F. Andreev, Sh. Yu. Azimov, Yu, P. Tarlakov, and N.F. Fedorov (1972) Infrared absorption spectra of synthetic britholites of the composition Me~+Nd6(Si04)6F2 where Me2+ is Mg, Ca, Sr or Ba. Sov. Phys. Dokl. 16, 798799. Sudarsanan, K. (1980) 1636-1639.

Structure

of hydroxylellestadite.

Acta Crystallogr.

B36,

Takemoto, K. and H. Kato (1968) Hydroxyl ellestadite produced by hydrothermal reaction containing calcium sulfate. Proc. 5th Intern'l. Sym. Chem. Cement, Tokyo. Vasileva, Z.V. (1958) Sulfur-bearing chemistry, 464-470, 1958).

apatites.

Geokhimiya,

368-373

(transl. Geo-

Vlasov, K.A. (1966) Mineralogy of Rare Elements Volume II, Geochemistry and Mineralogy of Rare elements and genetic types of their deposits. Translated from Russian; published by the Israel Program for Scientific Translations, 945 pp. Wuensch,

B.J.

(1972)

Sulfur.

Handbook of Geochemistry,

See section on URANYL SILICATES,

e SKLODOWSKITE.

See section ,on URANYL SILICATES,

eSODDYITE.

eSONOLITE,

4Mn2Si04'Mn(OH)2'

e SPESSARTINE,

• SPURRITE,

Mn3A12Si30l2'

Spurrite

P2lla;

low-pressure

occurs

A garnet;

this chapter.

of clinohumite;

see Chapter

see Chapter 10.

2.

The structure (1961).

the figure).

Z = 4.

0

in calc silicate

rocks which have undergone It is one of the diagnostic

;

high-temperature, minerals

of the

facies of contact metamorphism. was determined

Klevtsova

of the olivine

the "aragonite

a = 10.49, b = 6.705, c = 14.16 A, S = 101.32

contact metamorphism.

spurrite-merwinite

aCa2Si04

The Mn-analog

this chapter.

CaS (SiO 4) 2C03'

Monoclinic,

Belov

l6-A Crystal chemistry. In K.H. Wedepohl, Ed., Vol. II/2, p. l6Al-16A19. Springer-Verlag, Berlin.

by Smith et al. (1960) and Klevtsova

and Belov

(1961) describe

type alternating

The Ca in the "olivine

with layers of CaC0

3

layer" is 6-coordinated

layer" is 9-coordinated. 417

and

it as layers consisting of aragonite whereas

of (see

the Ca in

e SPURRITE,

continued

An xz projection of spurrite. The true monoclinic cell is indicated on the pseudo-orthorhombic motif. Inside the C03 triangles and in each of the two kinds of Si04 tetrahedra the heights of the central atoms are indicated by their y coordinates. Ca III octahedra are situated along the height of the cell in pairs one above the other with the coordinates y ± 0.05, 0.50 ± 0.05 and the Ca IV and Ca V octahedra also overlap each other with y coordinates near to 0 and to 0.50. The Ca I and Ca II polyhedra are not shown inside the monoclinic cell. They are distributed above and below the two types of tetrahedra (Si I and Si II) and are illustrated on the left of the diagram. From KletsovR et al. (1961). Klevtsova, R.F. and N.V. Belov (1961) Phys. Crystallogr. 5, 659-667.

Crystal

structure

of spurrite.

Sov.

Smith, J.V., I.L. Karle, H. Hauptman and J. Karle (1960) The crystal structure of spurrite, CaS(Si04)2C03' II. Description of structure. Acta Crystallogr. 13, 454-458.

e SWAMBOWITE.

eTEPHROITE,

eTHORITE,

See section on URANYL SILICATES,

Mn Si0 . 2 4 ThSi0 . 4

eTITANORHABDOPHANE.

eTOMBARTHITE,

An olivine;

see Chapter

An actinide orthosilicate;

11.

see Chapter

See TUNDRITE, this chapter.

YH[Si0 ]. 4

See Chapter

3.

418

this chapter.

4.

eTUNDRITE,

Na2ce2Ti02[Si041(C03)2'

=

100001';

a = 7.560, b = 13.957, c

pI;

Triclinic, y

Z

=

Since its description has had a number structure

in 1963 as the mineral

of proposed

determination

silico-carbonate

A;

5.040

101007',

a

S

1.

formulas.

by Shumyatskaya

of titanium

titanorhabdophane,

tundrite

The one given is based on a crystal

et al. (1976).

Tundrite

and the rare earth elements,

is an alkali

principally

Ce and La,

but Nd-rich material

has been reported (tundrite-Nd). Natural tundrites exhibit 3 substitution Ce + + Ti4+ = Ca2+ + NbS+. The structure of tundrite

the coupled

has edge-sharing a direction

chains parallel

in the

Si04 tetrahedra to form layers whose outer surfaces are covered by Ce-polyhedra and C03 groups. These layers are stacked

to b and are joined by interlayer

parallel

to c which are joined

by isolated

successively

the

Ti06 octahedra

elongated

habit of tundrite

Na atoms.

This structure

to c and its perfect

parallel

explains

(010) cleavage.

Shumyatskaya, N.G., A.A. Voronkov, V.V. Ilyukhim and N.V. Belov (1976) Tundrite, Na2Ce2Ti02[Si04](C03)2 - refinement of the crystal structure and chemical formula. Sov. Phys. Crystallogr. 21, 399-405.

e URANYL

SILICATES

The uranyl interpreted

silicate

group of minerals

as being secondary

environments

as alteration

in origin,

products

mulas are based on crystal

determinations

papers.

earlier

studies -- as well as information

pletely

characterized

chemistry variable member

has been reviewed amounts

of water,

compositions.

variations

substances,

recently

Systematic

about other related,

variation

silicates

are divided

for

properties

with small

that some substitutions

occur.

(Table 1).

edge-sharing,

equatorial,

dipyramid

pentagonal

The basic structural

(see the figures). 7 The U07 coordination polyhedron has two oxygens with interatomic distances of about 1.8 A, which are the uranyl oxygens, nearly perpendicular to the

pentagonal

U0

Except

nearly end-

into three groups by Stohl and Smith

(1981) on the basis of their U:Si ratios unit is a chain of edge-sharing

but incom-

(1981).

indicate

of physical

argu-

based on

(1958); their crystal

by Stohl and Smith of these minerals

among Ca, K, Pb, Mg and Cu suggests

The uranyl

chemical

mineralogy,

was given by Frondel

analyses

Their for-

or crystal

Their systematic

They are

supergene

of other uranium minerals.

structure

ments made in the referenced

are listed in Table 1. forming in oxidized,

pentagonal

coordination

bipyramids

ring of oxygens.

polyhedra 419

The distorted,

is better written

(U0 )05' 2

The

• URANYL SILICATES,

continued

[

~~ ~ e ~ '"

,~

OJ

.c

.

'"

o

~I

'"

"'o

'"

4-
.

'µ'r-I Q) Clj