Mineralogy [Third edition, Pearson new international edition] 1292039116, 1269374508, 9781292039114, 9781269374507, 9781292054841, 1292054840

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Pearson New International Edition Mineralogy Dexter Perkins Third Edition

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ISBN 10: 1-292-03911-6 ISBN 10: 1-269-37450-8 ISBN 13: 978-1-292-03911-4 ISBN 13: 978-1-269-37450-7

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Printed in the United States of America

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Table of Contents Glossary Dexter Perkins

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1. Elements and Minerals Dexter Perkins

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2. Crystallization and Classification of Minerals Dexter Perkins

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Crystallization and Classification of Minerals Color Plates Dexter Perkins

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3. Mineral Properties: Hand Specimen Mineralogy Dexter Perkins

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Mineral Properties: Hand Specimen Mineralogy Color Plates Dexter Perkins

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4. Optical Mineralogy Dexter Perkins

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Optical Mineralogy Color Plates Dexter Perkins

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5. Igneous Rocks and Silicate Minerals Dexter Perkins

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Igneous Rocks and Silicate Minerals Color Plates Dexter Perkins

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6. Sedimentary Minerals and Sedimentary Rocks Dexter Perkins

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Sedimentary Minerals and Sedimentary Rocks Color Plates Dexter Perkins

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7. Metamorphic Minerals and Metamorphic Rocks Dexter Perkins

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Metamorphic Minerals and Metamorphic Rocks Color Plates Dexter Perkins

215

8. Ore Deposits and Economic Minerals Dexter Perkins

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Ore Deposits and Economic Minerals Color Plates Dexter Perkins

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9. Crystal Morphology and Symmetry Dexter Perkins

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10. Crystallography Dexter Perkins

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11. Unit Cells, Points, Lines, and Planes Dexter Perkins

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12. X-ray Diffraction and Mineral Analysis Dexter Perkins

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13. Atomic Structure

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Dexter Perkins

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Descriptions of Minerals Dexter Perkins

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Descriptions of Minerals Color Plates Dexter Perkins

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Appendix: Classified List of Minerals Dexter Perkins

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Appendix: Mineral Identification Tables Dexter Perkins

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Appendix: Minerals Separated by Optic System and Sign, and Ordered by Index of Refraction Dexter Perkins

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Appendix: Minerals Ordered by Birefringence and Interference Colors in Thin Section Dexter Perkins

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Appendix: Minerals Ordered by Hardness Dexter Perkins

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Appendix: Minerals Ordered by Specific Gravity Dexter Perkins

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Coordination Numbers and Effective Ionic Radii Dexter Perkins

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List of Mineral Properties Dexter Perkins

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Periodic Table of the Elements Dexter Perkins

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Index

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III

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GLOSSARY Absolute hardness. A numerical measure of a mineral’s hardness; typically determined by indentation measurements (c.f. relative hardness). Accessory mineral. A mineral present in small amounts in a rock, unimportant for rock naming or classification. Accessory plate. A plate that may be inserted in the tube of a polarizing light microscope to produce interference colors of known birefringence. Typically made of quartz, gypsum, or mica. Acicular. Having a needle-like shape. Actinide. Elements (such as Th, Pa, and U) with atomic numbers 90 through 103 and valence electrons in 5f orbitals.

Andesite. An extrusive igneous rock of intermediate composition containing plagioclase as the only major feldspar; minor K-feldspar or quartz, pyroxene, biotite, and hornblende may be present. Angle of incidence. The angle that an impinging ray makes with a normal to an interface. Angle of refraction. The angle that a refracted ray makes with a normal to an interface. Anhedral. A crystal that lacks well-developed crystal faces or that has rounded or irregular form due to crowding by adjacent crystals. Anion. An ion having a negative charge.

Acute bisectrix. A line bisecting the angle formed by the two optic axes in a biaxial mineral.

Anionic complex. A tightly bonded, negatively charged molecular group; in mineral formulas, often surrounded by parentheses.

Acute bisectrix figure (Bxa). The interference figure seen when looking down an acute bisectrix.

Anisodesmic. Describing an ionic compound in which the ionic bonds are not all of the same strength.

Adamantine. A type of luster that is bright, sparkly, and shiny, similar to that of diamonds.

Anisotropic. Having different physical properties in different directions.

Aggregate (of crystals). A mass of crystals, of the same or different minerals, that may be physically separated, perhaps with some difficulty.

Anomalous interference colors. Interference colors that are not represented on the Michel Lévy Chart; typically associated with minerals of extremely low birefringence, such as chlorite.

Albite law. A common twin law in triclinic feldspars, often resulting in polysynthetic twins. Alchemy. Chemistry of the Middle Ages that combined science, magic, and philosophy. Alkali element. Any element (such as Li, Na, or K) of the first group in the Periodic Table of the Elements; alkali elements typically ionize to form monovalent cations.

Aphanitic. Having no mineral grains that are visible to the naked eye. Aqueous solution. A water-rich solution, usually containing dissolved elements or complexes. Arborescent. A term describing an aggregate of crystals having a tree-like appearance (see also dendritic).

Alkaline earth element. Any element (such as Be, Mg, or Ca) of the second group in the Periodic Table of the Elements; alkaline earth elements typically ionize to form divalent cations.

Arenite. General term for detrital sedimentary rocks composed of sand-sized grains and lithic fragments; includes sandstone, graywacke, arkose, and others (see also psammite).

Allochromatic. A term describing a mineral that gets its color from minor or trace elements (see also idiochromatic).

Asbestiform. A crystal habit characterized by fine threadlike, fibrous, or acicular crystals; more specifically, sometimes defined as a crystal habit with a length:diameter ratio of more than 3:1.

Alloy. A noncrystalline mixture of two or more metals. Alluvium. Unconsolidated sediment deposited by a stream.

Arkose. A feldspar-rich sandstone.

Amorphous. Having a random atomic structure (see also noncrystalline).

Asbestos. A general term referring to minerals that have an asbestiform habit; chrysotile, amosite, and crocidolite are typical asbestos minerals.

Amphibolite (facies). One of the principal metamorphic facies introduced by Eskola, corresponding to high-grade conditions of about 450 to 650 °C and 3 to 8 kbar.

Association (mineral). A group of minerals found together in a rock.

Amphibolite (rock). A metamorphic rock containing primarily hornblende and plagioclase. Analyzer. A polarizing filter that can be inserted in the upper column of a polarizing light microscope to view minerals under crossed-polarized light (see also upper polarizer). Anatexis. Partial melting of preexisting rock, generally associated with high-grade metamorphism.

Asterism. The play of colors seen in some minerals that produces a rayed or star-shaped figure when viewed in direct light; a star sapphire is one example. Atmophile. An element that tends to concentrate in the Earth’s atmosphere. Atomic absorption spectrophotometer. An analytical instrument in which composition is determined by measuring the absorption of characteristic wavelengths of light by an atomized and flamed sample.

From the Glossary of Mineralogy, Third Edition, Dexter Perkins. Copyright © 2011 by Pearson Education, Inc. Published by Pearson Prentice Hall. All rights reserved.

1

Glossary

Atomic number (Z). The number of protons in the nucleus of an atom of an element.

Becke line. A bright line, visible under a microscope, that separates substances of different refractive indices.

Atomic weight. The weight of an atom or compound in atomic mass units; generally close to the total number of protons and neutrons.

Bentonite. A clay-rich, earthy material formed by devitrification and alteration of tuff or volcanic ash; sometimes used more generally to refer to any clay deposit rich in montmorillonite.

Aufbau principle. The principle that states that electrons fill orbitals in a systematic way from the lowest energy orbitals to the highest. Augen. Large lenticular mineral grains or mineral aggregates in a foliated metamorphic rock. Augen gneiss. A gneiss containing augen. Aureole. A contact metamorphic zone surrounding an igneous intrusion (see also contact aureole). Authigenic. Formed or generated in place; used to describe minerals that form in a sediment or sedimentary rock after deposition of an original sediment.

Berman balance. A type of balance scale used to determine specific gravity. Bertrand lens. A lens that can be inserted in the tube of a polarizing light microscope to facilitate observation of interference figures. Biaxial. Describing a crystal having two optic axes and three principal indices of refraction (α, β, and γ). Such crystals belong to the orthorhombic, monoclinic, and triclinic crystal systems. Binary solution. A solid solution series that can be characterized by two end members.

Avogadro’s number. 6.022 * 1023, equivalent to the number of atoms or molecules in a mole.

Biogenic. Produced by living organisms or biological processes.

Axial ratio The ratio of unit cell lengths along each crystallographic axis, a : b : c.

Birefringence (property). The property of a crystal that causes double refraction.

Axis (crystallographic). One of three axes used to describe the geometry of a crystal lattice and the locations of points and planes in a unit cell.

Birefringence (value). The difference between the greatest and least indices of refraction of a crystalline substance.

Axis (rotational). A symmetry element that relates identical crystal faces or other things by rotation of 60°, 90°, 120°, 180°, or 360° about an axis.

Blocky. A term used to describe crystals that have a block-like appearance, generally with a nearly square cross section.

Backscatter electrons. High-energy electrons that are essentially reflected by the surface of a sample.

Blueschist (facies). One of the principal metamorphic facies introduced by Eskola, corresponding to high pressure– low temperature conditions.

Banded iron formation (BIF). A layered rock containing chert, silicate, carbonate, or oxide layers, giving a banded appearance. Barrovian facies series. The “normal” metamorphic facies series described by George Barrow; the most common sequence of metamorphic rocks that forms at mid-crustal depths. Basal cleavage. A term used to describe the cleavage in minerals such as micas that allows the mineral to break into plates or sheets. Basalt. An extrusive igneous rock of mafic composition containing plagioclase as the only major feldspar; clinopyroxene ; orthopyroxene ; olivine are typically present (see also gabbro).

2

Baveno twin. An uncommon twin law in feldspar.

Bladed. Having the appearance of blades.

Blueschist facies series. A facies series characterized by high pressures at relatively low temperatures; typical of subduction zone environments. Blueschist (rock). A vague term used to describe finegrained, bluish colored rocks diagnostic of the blueschist facies. Key minerals include blue amphiboles (glaucophane and riebeckite), lawsonite, jadeite, and aragonite. Body centered. Said of a unit cell that has an extra lattice point at its center. Body diagonal. A line passing through the center of a cube or other three-dimensional geometric shape and connecting opposite corners.

Basement rock. Metamorphic and igneous rocks that underlie sediments and sedimentary rocks observed at Earth’s surface; often, though not exclusively, of Precambrian age.

Bohr model of the atom. A fundamental model of an atom that describes electrons orbiting atomic nuclei in orbits associated with specific energy levels.

Basis. A sufficient set of symmetry operators for describing the symmetry of crystals (point symmetry) or of atomic structures (space symmetry).

Bomb. A laboratory reactor vessel used to conduct experiments and synthesize gems and minerals at high pressure and temperature.

Batholith. A large mass of intrusive igneous rock that solidified within the earth.

Bort. Diamond of low quality that is unsuitable as a gem but useful in industrial applications.

Mineralogy

Atomic mass unit (amu). Unit for expressing atomic mass, equal to approximately 1.6610 × 10 -27 kg.

Bauxite. Name given to a rock or a mineral-like material composed primarily of a mixture of aluminum oxides and hydroxides such as boehmite and gibbsite; bauxite is the most significant aluminum ore.

Glossary:

Atomic absorption spectroscopy (AAS). A technique for determining the concentration of a particular element in a sample that is based on light absorption by an atomized sample.

Glossary Botryoidal. A term used to describe a mineral habit that appears like a bunch of grapes. Boule. A oblong-shaped synthetic mineral crystal that is produced from the Verneuil technique. Bowen’s reaction series. A hypothetical series that describes the order of crystallization of minerals from a magma. Bragg law. A mathematical law that describes the relationship between the angle of diffraction (θ), X-ray wavelength (λ), and atomic plane spacing (d); nλ = 2dsinθ. Bravais lattices. The fourteen possible three-dimensional lattices that can describe mineral structures. Brazil law. A common type of twinning in quartz.

Cathode ray tube. Vacuum tube in which beams of highenergy electrons pass through magnetic fields and hit a fluorescent screen. Cation. An ion having a positive charge. Cementation. Lithification of clastic sediments resulting from the deposition or precipitation of minerals in the spaces between individual clastic grains; it may occur at the time of deposition or during diagenesis. Centered. Said of a unit cell that has (an) extra lattice point(s) at its center, in the center of its faces, or in the center of two opposing faces. Chain silicates. Silicate minerals characterized by SiO4 tetrahedra joining to form chains either one tetrahedron or two tetrahedra wide (see also inosilicates).

Breccia. A clastic sedimentary rock composed of large (> 2mm diameter) angular broken rock fragments in a finer grained matrix.

Chalcophile. An element that tends to concentrate in sulfide minerals and ores.

Bridging oxygen. An oxygen atom in a crystal structure that is shared by two or more equivalent coordinating polyhedra.

Characteristic radiation. High-intensity radiation of one or a few wavelengths emitted by the target of an X-ray tube; the wavelength(s) of characteristic radiation depend on the elements in the target.

Brittle. A term used to describe minerals that shatter or break easily when struck. Buchan facies series. A facies series characterized by similar temperatures but lower pressures than the Barrovian facies series, characterized by the presence of andalusite and sometimes cordierite. Brucite layer. A sheet of Mg(OH)6 octahedra in a layered crystal structure. Burial metamorphism. Metamorphism affecting a large region; caused by pressure related to depth in Earth and temperature related to geothermal gradient (see also regional metamorphism).

Chatoyancy. The play of colors seen in some minerals in which a silky sheen is seen to form a narrow band that changes position as the mineral is turned; for example, cat’s-eye chrysoberyl. Chemical precipitate. A solid that precipitates from an aqueous solution, typically due to supersaturation. Chemical sedimentary rock. A sedimentary rock composed primarily of material formed by precipitation from solution; for example, most limestones and all evaporites.

Cabochon. A gemstone that has been ground and polished into a domed shape.

Chemical sediments. Sediments produced by dissolution and precipitation resulting from chemical weathering; they may precipitate where weathering occurs or at a different place.

Calcine. To heat material, such as limestone, to high temperature, breaking down minerals and driving off carbon dioxide or other volatiles.

Chemical weathering. Type of weathering involving chemical reactions that transform or decompose minerals and rock.

Capillary. Having a hair-like or thread-like appearance (see also filiform).

Chert. A hard sedimentary rock composed primarily of cryptocrystalline silica, generally in the form of fibrous chalcedony with lesser amounts of quartz and opal.

Carbonate (mineral). A group of minerals with formulas characterized by (CO 3 )2- radicals. 2-

Carbonate (radical). The (CO 3 )

anionic group.

Carbonate (rock). A chemical sedimentary rock dominated by carbonate minerals; limestone or dolostone. Carbonation reaction. Reaction of a mineral or minerals with CO2 to produce a product carbonate mineral. Carlsbad twin. A common twin law in orthoclase, less common in other feldspars, often resulting in penetration twins. Cartesian coordinate system. An X-Y-Z coordinate system in which all axes are at 90° and the unit distances along all axes are equal. Cataclastic metamorphism. Metamorphism caused by a transient high-pressure condition such as a meteorite impact (see also shock metamorphism and dynamic metamorphism).

Chromophores. Elements that give minerals their color. Class. See crystal class. Clast. A mineral grain, lithic fragment, or organic remnant that is produced by mechanical weathering and becomes part of a clastic sediment or rock. Clastic. Being composed of fragments (clasts) derived from preexisting rocks. Clastic rock. Sedimentary rock formed by the lithification of clastic sediments; for example, sandstone, shale, and siltstone. Clausius-Clapeyron equation. An equation relating the slope of a reaction on a pressure-temperature diagram to the entropy and volume change of the reaction: dP/dT = ΔS/ΔV. Clay (grain size). A clastic fragment of any composition smaller than silt, having a diameter less than 1> 256 mm.

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Glossary

Clinonet. A two-dimensional lattice characterized by two translations of different magnitudes at nonspecial angles to each other. Clinopyroxene. Monoclinic pyroxene subgroup dominated by end members diopside and hedenbergite. The most common of all pyroxenes. Closest packing. The most efficient way to pack like atoms together in three dimensions; each atom is surrounded by 12 others. Colloform. Appearing as spherical or hemispherical shapes made of radiating crystals (see also globular). Color. A sensation produced by different wavelengths of light hitting the eye. Colorimetric analysis. Quantitative chemical analysis by color using a colorimeter. Columnar. Having the appearance of an aggregate of slender, elongated individual crystals, nearly parallel in arrangement. Complex twin. A twin composed of more than two individual crystals. Compositional zoning. Variation in the composition of a crystal, typically from core to margin (see also zoning). Composition plane. A plane that divides two twin domains in a twinned crystal. Compound (chemical). A substance of fixed atomic proportions made by the combination of two or more elements. Concentration factor. The extent to which an element must be concentrated above normal crustal levels to make mining it profitable. Conchoidal fracture. A type of fracturing that produces curved surfaces similar to when glass breaks; for example, quartz has a conchoidal fracture. Condenser. A lens, or several lenses, that may be inserted in the substage of a polarizing light microscope to cause light rays to converge on a sample (see also condenser lens). Condenser lens. See condenser. Conglomerate. A coarse-grained clastic sedimentary rock with fragments larger than 2 mm in diameter in a fine-grained matrix; the equivalent of lithified gravel. The clasts are rounded in conglomerates in contrast with breccias. Conoscopic illumination. Describing the strongly convergent light produced by the insertion of a condensing lens in a polarizing light microscope substage. Constructive interference. The addition of two waves that are in phase with negligible or no loss of energy.

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Contact metamorphism. Metamorphism localized around an igneous rock body; primarily in response to heat and flowing fluids. Contact twin. A twin in which two individuals are symmetrically arranged about a twin plane giving the appearance of two crystals in contact with each other. Continuous radiation. The low-intensity radiation covering a range of wavelengths that is produced by an X-ray tube; continuous radiation provides the background for characteristic radiation. Continuous side (Bowen’s reaction series). The side of Bowen’s reaction series characterized by plagioclase. Coordinating polyhedron. Polyhedron formed around an atom or ion by connecting the centers of the coordinated atoms or ions. Coordination number. Number of neighboring atoms to which an atom is bonded. Coquina. A soft, whitish limestone made up of broken sea shells and corals. Country rock. Rock intruded by and surrounding an igneous intrusion. Coupled substitution. Simultaneous substitution of two or more different ions in a structure in such a way that charge balance is maintained; for example, the substitution of Ca2+Al3+ for Na+Si4+ in plagioclase. Covalent bond. An ideal chemical bond that involves the sharing of orbital electrons between elements that have little or no difference in electronegativity. Cover slip. A thin piece of glass that is placed over grains and liquid to make a grain mount. Critical angle. The angle of incidence that yields an angle of refraction of 90°. Crossed polars (XP). The condition caused when the upper polarizer is inserted in a polarizing light microscope. Cryptocrystalline. A term describing a material containing generally submicroscopic grains whose crystalline nature is not easily determined. Crystal. A homogeneous solid body of an element, compound, or solid solution having a regularly repeating atomic structure that may be outwardly expressed as planar faces. Crystal classes. The 32 possible combinations of symmetry elements that a crystal may have; in modern usage, synonymous with the 32 possible point groups. Crystal morphology. The shape and form(s) of a crystal. Crystal structure. Spatial arrangement of atoms or ions, and their bonds, in a crystal. Crystal structure determination. Determination of the spatial arrangement of atoms and their bonds in a crystal. Crystal system. One of the six distinct coordinate systems used to describe minerals: cubic, orthorhombic, tetragonal, hexagonal, monoclinic, and triclinic. The trigonal subdivision

Mineralogy

Cleavage. The breaking of a mineral along a set of parallel, identical atomic planes.

Contact aureole. A contact metamorphic zone surrounding an igneous intrusion (see also aureole).

Glossary:

Clay (mineral). Member of a group of loosely defined hydrous sheet silicates formed primarily by alteration or weathering of primary silicates. The most common clays belong to the illite, kaolinite, or montmorillonite groups.

Glossary of the hexagonal system is sometimes counted as a separate crystal system.

Dehydration reaction. A reaction the liberates H2O from a carbonate mineral.

Crystalline. Having a crystal structure; having a regular arrangement of atoms characterized by a space lattice.

Dendritic. A term describing an aggregate of crystals having a tree-like appearance (see also arborescent).

Crystallographic axis. One of three axes used to describe the geometry of a crystal lattice and the locations of points and planes in a unit cell.

Density. The quantity of matter in a unit volume; mineral densities are typically given in units of gm/cm3

Cube. A closed form of six identical square faces at 90° to each other; a form of crystal class 4/m32/m.

Destructive interference. The addition of two outof-phase waves resulting in a total, or significant, loss of energy.

Cubic. Having a cube shape or belonging to the cubic system.

Detrital. Referring to a product of mechanical weathering.

Cubic (cleavage). A term used to describe three equal cleavages at 90° to each other; for example, halite has cubic cleavage. Cubic (coordination). The bonding of an ion to eight others arranged so that connecting their centers forms a cube. Cubic (system). A crystal system characterized by lattice symmetry 4/m 32/m. Cubic closest packing. Closest packing of atoms in a pattern similar to a face-centered cubic lattice; closest packing equivalent to stacking closest packed layers in an ABCABC sequence. Cumulate. A layer of minerals accumulated by gravity settling of crystals as they form in a magma chamber.

Detrital sedimentary rock. Rock formed by lithification of detrital sediments. Detritus. Broken-up material resulting from mechanical weathering. Diagenesis. Chemical, physical, and biological changes that affect sediment or sedimentary rocks after initial deposition, but excluding weathering or metamorphism. Diamagnetism. A property of minerals that causes a small negative reaction (repulsion) to a magnet. Diamond (shape). A parallelogram having four sides of equal length and no angles of 90°. Diamond lattice. See diamond net.

Cyanide method. A method for extracting valuable metals from ore that involves hydrogen cyanide.

Diamond net. A two-dimensional lattice characterized by two translations of the same magnitude at nonspecial angles to each other.

Cycle. One complete upward and downward motion by a wave.

Diaphaneity. The ability of a mineral to transmit light; often described as transparent, translucent, or opaque.

Cyclic twinning. Repeated twinning of three or more individuals according to the same twin law but with the twin axes or twin planes not parallel, usually producing a twinned crystal in which twin domains are related by apparent rotational symmetry.

Diaphragm. An adjustable opening used to control the size of a light beam in a polarizing light microscope.

Cyclosilicates. Silicate minerals characterized by SiO4 tetrahedra joining to form rings (see also ring silicates). Czochralski process. A method of making synthetic gems that involves a seed crystal drawing material out of a melt.

Diatomite. To come. Dichroism. Pleochroism of a mineral that is observed as two different colors. Diffraction. Apparent bending of radiation by evenly spaced atoms, slits, or gratings. Diffraction grating. A grating that causes diffraction. Diffraction slit. A slit that causes diffraction.

D-value. The distance between adjacent planes with the same Miller indices.

Diffractometer. An instrument that records X-ray diffraction patterns.

Dacite. An extrusive igneous rock of silicic composition that contains more plagioclase than K-feldspar; biotite and hornblende are typically present (see also granodiorite).

Dioctahedral. Describing a layered mineral structure in which only two of three available octahedral sites are occupied.

Daughter element. The product element of radioactive decay. Daughter isotope. The product isotope of radioactive decay. Dauphiné law. A common type of twinning in quartz. Decarbonation reaction. A reaction that liberates CO2 from a mineral.

Diorite. An intrusive igneous rock of intermediate composition containing plagioclase as the only major feldspar; minor K-feldspar or quartz, pyroxene, biotite, and hornblende may be present. Diploid. A closed cubic form of 24 quadrilateral faces; a form of crystal class 2/m3.

Defect. A flaw in an otherwise ideal crystal structure.

Dipyramid. A closed crystal form of 6, 8, 12, 16, or 24 faces, comprising two pyramids related by a mirror plane of symmetry.

Degrees of freedom. The number of intensive variables that may be changed independently without causing a change in mineral assemblage or composition.

Discontinuous side (Bowen’s reaction series). The side of Bowen’s reaction series characterized by olivine-pyroxeneamphibole-biotite.

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Glossary Disequilibrium. The state of being in the process of reacting so that the relative amounts of reactants and products are changing.

Edge diagonal. A line passing through the center of a cube or other three-dimensional geometric shape, and connecting the centers of opposite edges.

Dispersion. A difference in wave velocity for different wavelengths.

Edge dislocation. A kind of line defect caused by a terminated row of atoms.

Disphenoid. A closed crystal form comprising two sphenoids related by 222 symmetry.

Edge sharing. The sharing of two atoms or ions by two adjacent coordinating polyhedra; the coordinating polyhedra appear to be sharing an edge.

Divalent. Having a charge of ;2. Divariant field. A region on a phase diagram characterized by two degrees of freedom. Divergent (crystals). Slender crystals emanating from a common point (see also radiating). Dodecahedral (coordination). 12-fold coordination. Dodecahedron. A 3-dimensional geometric shape characterized by 12 identical faces; one of the common forms of the cubic system. Dolostone. A chemical sedimentary rock composed primarily of dolomite. Domain. A region within a crystal having an atomic orientation that differs from other regions within the crystal. Dome. An open crystal form composed of two nonparallel faces related by a mirror. Dop. A stick-like device that holds a gem crystal for grinding on a wheel. Double-chain silicates. Silicate minerals (amphiboles) charactized by SiO4 tetrahedra joining to form chains two tetrahedra wide. Double refraction. The ability of a mineral to split ordinary light into two waves of different velocities and polarization. Doubly primitive. Term describing a unit cell containing a total of two lattice points. Drusy. Having surfaces coated with fine crystals. Ductile. A term used to describe the tenacity of minerals that are capable of being drawn into a wire-like shape. Dull. A type of luster that does not reflect significant amounts of light or show any play of colors. Dunite. An ultramafic intrusive rock in which the only major mineral is olivine; chromite is typically present as an accessory mineral.

Elastic. A term used to describe minerals that return to their original shape after bending. Electromagnetic radiation. Emission or transfer of energy in the form of waves; includes X rays, visible light, infrared light, radio waves, and television waves. Electron. An extremely small atomic particle having little mass that is the smallest negative electric charge occurring in nature. Atoms have electrons orbiting around a nucleus. Electron cloud. The space occupied by electrons surrounding an atomic nucleus. Electronegativity. Measure of the tendency of elements to acquire electrons. Electron microprobe. An analytical instrument in which a finely focused electron beam hits a sample, causing emission of elemental characteristic radiation. Electron microscope. A microscope that is in some ways similar to a conventional light microscope but achieves much greater resolving power by using a beam of electrons to illuminate the sample instead of light. Electron probe micro analyzer (EPMA). See electron microprobe. Electrostatic valency principle (Pauling’s second rule). The strength of ionic bonds to any ion is equal to the ion’s charge divided by its coordination number. Element. A basic chemical unit composed of atoms having the same atomic number; elements cannot be separated into simpler parts by chemical means. Elliptic. A term describing crystals that are very small ellipsoids. Enantiomorphic pair. A term describing two crystals whose atomic structures are mirror images of each other.

Dynamic metamorphism. Metamorphism caused by a transient high-pressure condition such as a meteorite impact (see also shock metamorphism and cataclastic metamorphism).

End centered. A term describing a unit cell with an extra lattice point in each of two opposing faces.

E ray. See extraordinary ray.

Energy dispersive X-ray spectroscopy (EDS). An analytical technique that involves measuring the energy of X-rays emitted, in order to identify the elements present and their concentrations, in a sample.

Eclogite (facies). A high-pressure/high-temperature metamorphic facies characteristic of the mantle. Eclogite (rock). A high-pressure/high-temperature rock containing Mg-rich garnet (pyrope) and Na-rich clinopyroxene (omphacite); mostly of mantle origin.

6

Effervescence. A bubbling reaction; the term used to describe the reaction of calcite with dilute hydrochloric acid.

End member. An ideal chemical formula representing one limit of a solid solution.

Energy level. The energy associated with a particular electron orbit in an atom.

Mineralogy

Dissolution. The process of dissolving.

Effective ionic radius. Radius of a spherical volume effectively occupied by an ion in a particular structure.

Glossary:

Disseminated deposit. An ore deposit in which the ore mineral is scattered throughout a host rock.

Glossary Enthalpy (H). A thermodynamic variable related to the Gibbs free energy.

Face centered. A term describing a unit cell with an extra lattice point in the center of each of its faces.

Entropy (S). A thermodynamic variable representing the degree of randomness or disorder in a system, which are related to the system’s ability to absorb energy without increasing its temperature.

Face sharing. The sharing of three atoms or ions by two adjacent coordinating polyhedra; the coordinating polyhedra appear to be sharing a face.

Epigenetic. Refers to a mineral deposit that is emplaced after its host rocks already exist. Equant. Having approximately the same dimensions in all directions. Equilibrium. A static state of a chemical system in which the relative amounts and compositions of phases present do not undergo changes with time. Essential mineral. A mineral in a rock that is necessary for the rock to be classified or named as it is. Euhedral. A crystal that is completely bounded by welldeveloped crystal faces and whose growth was not restrained by adjacent crystals. Evaporite (mineral). Minerals that may form by precipitation from aqueous solution under normal Earth surface conditions; for example, halite, sylvite, and gypsum. Evaporite (rock). A chemical sedimentary rock formed by evaporation of water; for example, massive gypsum or salt beds. Evaporite deposit. Mineral deposit formed by evaporation of water. Even (fracture). A fracture that produces smooth planar surfaces. Exhalitive. A hydrothermal deposit created at the Earth’s surface; generally one that forms on the ocean floor from springs. Expandable clay. One of a group of clay minerals (smectites) that can expand their structure to accommodate excess water or other chemical components. Exsolution. The separating of an initially homogeneous mineral solid solution into two (or more) zones of distinct mineral phases; for example, the formation of perthite from a homogeneous feldspar during cooling. Exsolution lamellae. Fine parallel zones of different compositions resulting from exsolution. Extinct (mineral grain). A term describing a birefringent mineral grain oriented so that it appears dark when viewed under crossed polars. Extinct (X-ray peak). A term describing an X-ray peak missing from a diffraction pattern due to destructive interference. Extinction (X-ray). The systematic absence of a related group of X-ray peaks in a diffraction pattern. Extinction angle. The angle, measured under crossed polars, between the position of extinction and a cleavage, long dimension, or other direction in a crystal. Extraordinary ray (E ray). In a uniaxial crystal, the ray of light that vibrates in a plane containing the optic axis. Extrusive rock. An igneous rock that crystallizes at or very near Earth’s surface, typically characterized by relatively coarse crystal size (see also volcanic rock).

Facet. A polished face on a gemstone. Facies (metamorphic). A range of pressure-temperature conditions characterized by one or more specific mineral assemblages. Family of planes. An infinite number of planes, parallel and spaced equally, all characterized by the same Miller index. Fast ray. The fastest of the two rays produced by double refraction. Feldspar. Any of a group of common framework silicates that are found in rocks of many kinds and are characterized by Al- and Si-tetrahedra connected by bonds to Ca, Na, or K. Feldspathic. An adjective describing a mineral aggregate that contains feldspar. Feldspathoid. A mineral group containing framework silicates, closely related to the feldspar group but containing less silica. Felsic. A general adjective referring to igneous rocks having light colored minerals in their mode. Ferromagnetism. A type of magnetic order, characteristic of iron, that causes a mineral to respond strongly to a magnetic field. Fibrous (cleavage). A term describing a cleavage that allows a crystal to be broken into fibers. Fibrous (crystals). Having the appearance of being composed of fibers. Filiform. Having a hair-like or thread-like appearance (see also capillary). Fissility. The rock property of breaking easily along closely spaced planes; often used to describe shale or schist. Flash figure. The interference figure observed when the optic axis (uniaxial mineral) or the optic plane (biaxial mineral) are oriented parallel to the stage of a polarizing light microscope. Flexible. A term used to describe the tenacity of minerals that are bendable. Flood basalt. A laterally extensive and thick lava flow of basaltic composition. Fluorescence. A type of luminescence that occurs when minerals are exposed to ultraviolet light, X rays, or cathode rays, but ceases when the exposure ceases. Flux. A substance added to promote a chemical reaction or to lower the melting temperature of a material without changing the chemistry of the important phases that are present. Flux method. A method of synthesizing gems or other minerals by growing them in an inert flux. Foliated. Having planar or sheet-like properties. Foliation. A planar fabric or texture. Fool’s gold. Common name for pyrite.

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Glossary

Fracture. Breaking of a mineral other than along planes of cleavage. Framework silicates. Silicate minerals characterized by SiO4 tetrahedra joining to form three-dimensional networks (see also tectosilicates and network silicates). Frenkel defect. A defect caused when an atom in a crystal structure is displaced from its normal position to a different position. Gabbro. An intrusive igneous rock of mafic composition containing plagioclase as the only major feldspar; clinopyroxene ; orthopyroxene ; olivine are typically present (see also basalt).

Gneiss. A foliated metamorphic rock showing contrasting bands of light- and dark-colored minerals. Goldich’s weathering series. A hypothetical series that describes the order of weathering of minerals in outcrop; the series is essentially the opposite of Bowen’s reaction series. Goniometer. A calibrated instrument used to measure the angles between crystal faces, cleavages, or other planar features in crystals. Grade (metamorphic). The degree of metamorphism; generally equivalent to the temperature of metamorphism (see also metamorphic grade). Grade (ore). The concentration of ore minerals or elements in ore rock.

Gamma rays. Electromagnetic radiation of higher energy and shorter wavelength than X-rays; emitted by atomic nuclei.

Grain mount. Fine mineral grains on a glass slide surrounded by a liquid and covered with a cover slip.

Gangue. The waste minerals in an ore deposit.

Granite. An intrusive igneous rock of silicic composition containing 10% to 50% quartz and K-feldspar as the major feldspar; plagioclase, biotite, and hornblende may be present (see also rhyolite).

Gem. An especially fine or superlative specimen, often of mineralogical origin, usually having superb color, light properties, or shape; often a cut-and-polished stone that has value due to beauty, durability, rarity, or size; generally for use in jewelry or for ornamentation. Gemmy. Having a gem-like appearance; typically having a bright color, an attractive luster, or geometric shape. Gemstone. A gem of mineralogical origin. General angle. A nonspecial angle between crystal faces or symmetry elements. General form. For a given point group, a form that has the maximum possible number of faces and whose faces and face normals do not intersect at special angles. General point. On a stereo diagram, a point that is located at a general position, not coincident with an inversion center, a rotational axis, or a mirror plane. Geode. A hollow or partly hollow rock cavity lined by mineral material. Geothermometer. A mineral or mineral system with compositional variations that reflect the temperature at which it formed.

Granitic. A general adjective applied to any light-colored intrusive igneous rock or to any rock composition that generally resembles that of a granite. Granitoid. A general term for any coarse-grained light-colored igneous rock composed primarily of feldspar, quartz, mica, and hornblende. Granodiorite. An intrusive igneous rock of silicic composition that contains more plagioclase than K-feldspar; biotite and hornblende are typically present (see also dacite). Granular. Composed of many small grains. Granulite (facies). The metamorphic facies corresponding to the highest grades of regional metamorphism. Granulite (rock). A high-grade metamorphic rock containing orthopyroxene. Gravel. Clastic material with grains greater than 2 mm in diameter; may include boulders, cobbles, pebbles, or granules. Gravimetric analysis. An analytical technique that is based on the measurement of mass.

Gibbs free energy. A thermodynamic variable that describes the relative stability of a mineral or a mineral assemblage; also refers to the energy change associated with a chemical reaction.

Graywacke. General term used for clastic sedimentary rocks similar to sandstones but containing an inordinate amount of clays, rock fragments, or other material in addition to quartz and feldspar.

Gibbs phase rule. A consequence of the laws of thermodynamics: for any chemical system in equilibrium, the number of chemical components plus two is equivalent to the number of stable phases plus the number of degrees of freedom: C + 2 = P + F (see also phase rule).

Greasy (luster). A type of luster describing crystal faces or other surfaces that reflect light to give a play of colors similar to oil on water.

Gibbsite layer. A sheet of Al(OH)6 octahedra in a layered crystal structure. Glass. An amorphous solid material; in most cases, a metastable supercooled liquid.

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Globular. Appearing as spherical or hemispherical shapes, often made of radiating crystals see also colloform.

Greenschist (rock). A medium-grade metamorphic rock characterized by schistosity and green minerals including actinolite, chlorite, and epidote. Greenschist (facies). A medium-grade metamorphic facies characterized by conditions of about 300 to 500 °C and 2 to 8 kbar.

Mineralogy

Fractional crystallization. Separation of a crystallizing magma into compositionally different parts by the successive crystallization of different minerals (see also partial crystallization).

Glide plane. A compound symmetry operation that repeats a motif or other entity after a reflection and translation are combined.

Glossary:

Form. A set of identically shaped crystal faces related by symmetry.

Glossary Greenstone. A vague term used to describe any finegrained, low-grade green metamorphic rock; generally of basaltic composition. Greenstone belt. A metamorphic terrane characterized by the presence of low-grade metamorphosed volcanics and volcanogenic sediments and silicic to intermediate plutons