Mineralogy Terms

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accessory mineral: a mineral present in small amounts in a rock, unimportant for rock naming or classification
accesssory plate: a plate that may be inserted in the tube of a polarizing light microscope to produce interference of a known amountl 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
acute bisectrix: aline bisecting the angle formed by the two optic axes in a biaxial mineral
acute bisectrix figure (Bxa): the interference figure seen when looking down an acute bisectrix
adamantine: a type of luster that is bright, sparkly, and shiny similary to that of diamonds
aggregate (or crystals): a mass of crystals, of the same or different minerals, that may be physically separated, perhaps with some difficulty
albite twin: a common twin law in ticlinic feldspars, often resulting in polysynthetic twins
alchemy: chemistry of the Middle Ages that combind 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
Alkaline earth element: any element (such as Be, Mg, or Ca) of the second group in the Periodic Table of the Elementsl alkaline earth elements typically ionize to form divalent cations
allochromatic: a term descriving a mineral that gets its color from minor or trace elements (see also iodiochromatic)
alloy: a noncrystalline mixture of two or more metals
alluvium: unconsolidated sediment deposited by a stream
amorphous: having a random atomic structure (see also noncrystalline)
amphibolite (facies): one of the principal metamorphic facies introduced by Eskola, corresponding to high-grade conditions of about 450 - 650 and 3- 8 Kbar
amphibolite (rock): a metamorphic rock containing primarily hornblende and plagioclase
analyser: a polarizing filter that can be inserted in the upper column of a polarizing light microschope to view minerals under crossed-polarized light (see also upper polarizer)
anatexis: melting of preexisting rock
andesite: an extrusive igneous rock of intermiediate composition containing plagioclase as the only major feldspar; minor K-feldspar or quartz, pryoxene, 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 wit ha normal to an interface
anhedral: a crystal that lacks well-developed crystals faces or that has rounded or irregular form due to crowding by adjacent crystals
anion: an ion having a negative charge
anionic complex: a tightly bonded, negatively charged moleculr group; in mineral formulas, often surrounded by parentheses
anisodesmic: describing an ionic compound in which the ionic bonds are not all of the same strength
anisotropic: having different physical properties in different directions
anomalous interference colors: interference colors that are not represented on the Michel Levy Chart; typically associated with minerals of exteremely low birefringence, such as chlorite
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 descrving an aggregate of crystals having a treelike appearance (see also dendritic)
arenite: general term for detrital sedimentary rocks composed of sand-sized grains and lithic fragments; includes sandstone, graywacke, arkose, and others (see also psammite)
arkose: a feldsapr-rich sandstone
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 thant 3:1
asbestos: a genral term referring to minerals that have an asbestiform habitl chrysotile, amosite, and crocidolite are typical asbestos minerals
association (mineral): a group of minerals found together in a rock
asterism: the play of colors seen in some minerals that produces a rayed or star-shpaed 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 compoistion is determind by measuring the absorption of characterisitc wavelengths of light by an atomized and flamed sample
atomic mass unit (amu): unit for expressing atomic mass, equal to approximately 1.66x10^-24 grams
atomic number(Z): the number of protons in the nucleus of an atom of an element
atomic weight: the weight of an atom or compound in atomic mass unitsl generally close to the total number of protons and neutrons
Aufbaur principle: the principle that states that electrons fill orbitals in a systematic way from the lowest energy orbitals to the highest
augen: lagrge lenticular mineral grains or mineral aggregates in a foliated metamorphic rock
augen gneiss: a gneiss containing augen
authigenic: formed or generated in place; used to describe minerals that form in a sediment or sedimentary rock after deposition of an original sediment
Avogadro's number: 6.022x10^23, equivalent to the number of atoms or molecules in a mole
Axial ratio: the ration of unit cell lengths along each crystallographic axis, a:b:c
axis (crystallographic): one of the three edges of a chosen unit cell in a crystall lattice; the coordinate system used to describe points, lines, and planes in a crystal
axis (rotational): a symmetry element that relate identical crystals faces or other things by rotation of 60, 90, 120, 180, or 360 about an axis
Banded iron formation(BIF): a layered rock containing chert, silicate, carbonate, or oxide layers, giving a banded appearence
Basal cleavage: a term used to describe the cleavage in minerals such as micas that allows the ineral to break into plates or sheets
Basalt: an extrusive igneous rock of mafic composition containing plagioclase as the only major feldspar; clinopyroxene plus or minus orthopyroxene plus or minus olivine are typically present (see also gabbro)
basement (rock): metamorphic and igneous rocks that underlie sediments and sedimentary rocks observed at the Earth's surface; often, though not exclusively, of Precambrian age
basis: a sufficient set of symmetry operators for descriving the symmetry of crystals (translation-free symmetry) or of atomic structures (space sysmmetry)
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;l bauxite is the most significant aluminum ore
Baveno twin: an uncomomon twin law in feldspar
Becke line: a bright line, visible under a microscope, that separates substances of different refractive indices
bentonite: a clay-rich earthy materal formed by devitrification and alteration of tuff or volcaing ash; sometimes used more generally to refer to any clay deposit rich in montmorillonite
Berman blaance: a type of balance scale used to determine specific gravity
Betrand lens: a lends 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. 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
birefringence (property): the property of a crystal that causes double refraction
birefringence (value): the difference between the greatest and least indices of refraction
bladed: having the appearance of blades
blocky: a term used to describe crystals that have a blocklike appearance, generally with an approximately square cross section
blueschist (facies): one of the principal metamorphic facies introduced by Eskola, corresponding to high pressure-low temperature conditions
blueschist (rock): a vague term used to describe fine grained, bluish colored rock 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: aline passing through the center of a cube or other three-dimensional geometric shape and connecting opposite corners
Bohr model of the atom: a fundamental model of an atom that states that electrons orbit atomic nuclei in orbits associated with specific energy levels
bomb: a laboratory reactor vessel used to synthesize gems and minerals at high pressure and temperature
bort: dimond of low quality that is unsuitable as a gem but useful in industrial applications
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 magma
Bragg law: a mathematical law that describes the relationship between the angle of diffraction, x-ray wavelength, and atomic plane spacing
Bravais lattices: the fourteen possible three-dimensional lattices that can describe mineral structures
Brazil twin: a common type of twinning in quartz
Breccia: a clastic sedimentary rock composed of large angular broken rock fragments in a finer grained matrix
Bridging oxygen: an oxygen atom in a crystal structure that is shared by two or more equivalent coordinating polyhedra
brittle: a term used to describe minerals that shatter or break easily when struck
brucite layer: a sheet of Mg(OH)6 octahedra in a layered crystal structure
Buerger precession camera: an instrument designed to record single crystal diffraction patterns on film
burial metmorphism: metamorphism affecting a large region; caused by pressure related to depth in the Earth and temperature related to geothermal gradient (see also regional metamorphism)
Cabochon: a gemstone that has been ground and polished into a domed shape
calcine: the heat material, such as limestone, to high temerature, breaking down minerals and driving off carbon dioxide or other volatiles
capillary: having a hairlike or threadlike appearance (see also filiform)
carbonate (mineral): a group of minerals with formulas characterized by (CO3) 2- radicals
Carbonate (radical): the (CO3) 2- 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 commmon 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 90degree and the unit distances along all axes are equal
Cataclastic metamorphism: metamorphism caused by a transient high-pressure condition such as a meteor impact (see also shock metamorphism and dynamic metamorphism)
Cathode ray tube: Vacuum tube in which beams of high-energy 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 diagensis
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)
chalcophile: an element that tends to concentrate in sulfide minerals and ores
characteristic radiation: high-intensity radiatioin of one or a few wavelengths emitted by the target of an X-ray tubel the wave length(s) or characteristic radiation depend on the elements in the target
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 sedimenatray rock composed primarily of material formed by precipiation from solution; for example, most limestones and all evaporites
chemical sediments: sediments produced by dissolution and precipitaion resulting from chemical weathering; they may precipitate where weathering occurs or at a different place
chemical weathering: type of weathering involving chemical reactions that transform or decompose miinerals and rock
chert: a hard sedimentary rock composed primarily of cryptocrystalline silica, generally in the from of cibrous chalcedony with lesser amounts of quartz and opal
chromophores: elements that give minerals their color
clast: a mienral grain, lithic fragment, or organic remnant that is produced by mechanical weathering and bcomes part of a clastic sediment or rock
clastic: being composed of grafments (clasts) derived from preexisting rocks
clastic rock: sedimentray rock formed by the lithification of clsatic sediments; for example, sandstone, shale, and siltstone
Clausius-Clapeyron equation: an equation relating the slope of a reaction on a prssure-temperature diagram to the entropy volume change of the reaction
clay (grain size): a clastic fragment of any cmposition smaller than silt, having a dimaeter less that 1/256 mm
clay (mineral): member of a group of loosely defind hydrous sheet silicates formed primarily by alteration or weather of primary silicates. The most common clays belong to the illite, jaolinite, or montmorillonite groups
cleavage: the breaking of a mineral along a set of parallel identical atomic planes
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
closet packing: the most effecient way to pack like atoms together in three dimensions; each atom is surrounded by 12 others
colloform: appearing as spherical or hemispherical shpaes made of radiating crystals (see also globular)
color: a sensation produced by different wavelengths of light hitting the eye
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 crysta, typically from core to margin (see also zoning)
compound (chemical): a substance of fixed atomic proportions made by the combination of two or more elements
concentration fact: the extent to which an element must be concentrated above normal crustal levels to make minig it profitable
conchoidal: a term describing fracturing that produces curvged 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 condensing lens)
condensive lens: see condenser...
conglomerate: a coarse-grianed clastic sedimentary rock with fragments larger that 2 mm in diameter in a fine-grained matrix; the equivalent of lithified gravel. The clats 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
contact aureole: a contact metamorphic zone surrounding an igneous intrusion (see also aureole)
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
Continuous radiation: the low-intensity radiation covering a range of wavelengths , produced by and 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 ocnnecting the centers of the coordinated atoms or ions
coordination number: number of neighboring atoms to which and atom is bonded
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 Ca, Al, for ?Na, Si, in albite
covalent bond: an ideal chemical bond that involves the sharing or 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 degrees
crossed polars: 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 homogenuous 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, practically synony mous with the 32 possible point groups
crystal morpholofy: the shape and form(s) of a crysral
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: cubic, orthorhombic, tetragonal, hexagonal, monoclinic, and triclinic. The trigonal subdivision of the hexagonal system is sometimes counted as separate crystal system.
crystalline: having a crystal structure; having a regular arrangement of atoms characterized by a space lattice
crystallographic axis: a direction corresponding to one of the three edges of a chosen unit cell in a crystal lattice
cube: a closed form of six identical square faces of 90degree to each other
cubic: having a cube shape or belonging to the cubic system
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/m32/m and containg point groups with symmetry no greater than 4/m32/m; one cell parameter (a) is needed to describe the shape and size of a cubic unit cell
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
cyanide method: a method for extracting valuable metal ore that involves hydrogen cyanide
cycle: one complete upward and downward motion by a wave
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 aparent rotational symettry
cyclosilicates: silicate minerals characterized by SiO4 tetrahedra joining to from rings (see also ring silcates)
Czochralski process: a method of making synthetic gems that involves a seed crystal drawing materals out of a melt
d-value: the distance betwen adjacent planes with the same Miller indices
dacite: an extrusive igneous rock of silicic composition that contains more plagioclase than K-feldspar; biotite and hornblende are typically present (see also granodiorite)
daughter element: the product element of radioactive decay
daughter isotope: the product isotope of radioactive decay
Dauphine twin: a common type of twinning in quartz
Debeye-Scherrer camera: the most commonly used and most versatile camera for obtaining powder diffraction patterns
decarbonation reaction: a reaction that liberates CO2 from a mineral
defect: a flaw in an otherwise ideal crystal structure
degrees of freedom: the number of intensive variables that may be changed independently without causing a change in mineral assemblage or composition
dehydration reaction: a reaction that liberates H2O from a carbonate mineral
dendritic: a term describing an aggregate of crystals having a treelike appearance (see also arborescent)
density: he quantity of matter in a unit volume; mineral densities are typically given in units of gm/cm3
destructive interference: the addition of two out-of-phase waves resulting in a total, or significant, loss of energy
detrital: referring to a product of mechanical weathering
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 sedimnetary 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 at 90 degrees
diamond lattice: see diamond net
diamond net: a two-dimensional lattice characterized by two translations of the same magntude at nospecial angles to each other
disphaneity: the ability of a mineral to transmit light; often described as transparent, translucent, or opaque
diaphragm: an adjustable opening used to control the size of a light beam in a polarzing light microscope
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
diffractometer: an instrument that recods x-ray diffraction patters
dioctehedral: describing a layered mineral structure in which only two or three available octahedral sites are occupied
diorite: an intrusive igneous rock of intermediate compositio containing plagiocalse 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 from of crystal class 2/m3
dipyramid: a closed crystal form of 6, 8, 12, 16 or 24 faces, comprising two pyramids related by a mirror plane of symmetry
discontinuous side (Bowen's reaction series): the side of Bowen's reaction series characterized by olivine-pyroxene-anphibole-biotite
disequilibrium: dispersion
dispersion: a difference in wave velocity for different wave lengths
disphenoid: a closed crystal form comprising two sphenoids related by 222 symmetry
disseminated deposit: an ore deposit in which the ore mineral is scattered throughout a host rock
dissolution: the process of dissolving
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 closed cubic form of 12 faces that may have any of a number of shapes and point group symmetries
dolostone: a chemical sedimentary rock composed primarily of dolomite
domain: a region within a crystal having a structure or 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 sticklike device that holds a gem crystal for grinding on a wheel
double chain silicates: silicate minerals characterzied by SiO4 tetrahedra joining to form chains two tetrahedra wide (see also amphibole)
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 mienrals that are capable of being drawn into a wirelike 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 typicall ypresent as an accessory mineral
dynamic metamorphism: metamorphism caused by a transient high-pressure condition such as a meteor impact (see also shock metamorphism and cataclastic metamorphism)
E-ray: see extraordinary ray
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
edge diagonal: a line passing through the center of a cube or other three-dimensional geometirc shape, and connecting the centers of opposite edges
edge dislocation: a kind of line defect caused by a terminated roc of atoms
edge sharing: the sharing of two atoms or ions by two adjacent coordinating polyhedra; the coordinating polyhedra appear to be sharing an edge
effective ionic radius: radius of a spherical volume effectively occupied by an ion in a particular structure
effervescence: a bubbling reacton; the term used to describe the reaction of calcite with dilute hydrochloric ace
elastic: a term used to describe mienrals that return to their original shpae after bending
electromagnetic radiation: emission or transfer of energy in the form of waves; includes x-rays, visible light, infrared light, radiowaves, and television waves
electron: an extremely small atomic particle having little mass and 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
electron microprobe: an analytical instrument in which a finely focused electron beam hits a sample, causing emission of elemental characterisitc radiation
electronegativity: measure of the tendency of elements to acquire electrons
electrostatic valency principle (Pauling's rule 2): the strength of an ionic bond is equal to its ionic 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: a term describing two crystals whose atomic structues are mirror images of each other
end centered: a term describing a unit cell with an extra lattice point in each of two opposing faces
end member: an ideal chemical formula representing one limit of a solid solution
energy level: the enrgy associated with a particular electron orbit in an atom
enthalpy: a thermodynamic variable related to the Gibbs free energy
entropy: a thermodynamic variable representing the degree of randomness or disorger in a system
epigenetic: refers to a mineral deposit that is emplaced after its host rock already exists

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