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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.
having a needle like shape
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
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
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
a term descriving a mineral that gets its color from minor or trace elements (see also iodiochromatic)
a noncrystalline mixture of two or more metals
unconsolidated sediment deposited by a stream
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
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)
melting of preexisting rock
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
a crystal that lacks well-developed crystals faces or that has rounded or irregular form due to crowding by adjacent crystals
an ion having a negative charge
anionic complex
a tightly bonded, negatively charged moleculr group; in mineral formulas, often surrounded by parentheses
describing an ionic compound in which the ionic bonds are not all of the same strength
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
having no mineral grains that are visible to the naked eye
aqueous solution
a water-rich solution, usually containing dissolved elements or complexes
a term descrving an aggregate of crystals having a treelike appearance (see also dendritic)
general term for detrital sedimentary rocks composed of sand-sized grains and lithic fragments; includes sandstone, graywacke, arkose, and others (see also psammite)
a feldsapr-rich sandstone
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
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
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
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
lagrge lenticular mineral grains or mineral aggregates in a foliated metamorphic rock
augen gneiss
a gneiss containing augen
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
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
a sufficient set of symmetry operators for descriving the symmetry of crystals (translation-free symmetry) or of atomic structures (space sysmmetry)
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
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
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
having the appearance of blades
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
a laboratory reactor vessel used to synthesize gems and minerals at high pressure and temperature
dimond of low quality that is unsuitable as a gem but useful in industrial applications
a term used to describe a mineral habit that appears like a bunch of grapes
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
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
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)
a gemstone that has been ground and polished into a domed shape
the heat material, such as limestone, to high temerature, breaking down minerals and driving off carbon dioxide or other volatiles
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
an ion having a positive charge
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
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)
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
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
a hard sedimentary rock composed primarily of cryptocrystalline silica, generally in the from of cibrous chalcedony with lesser amounts of quartz and opal
elements that give minerals their color
a mienral grain, lithic fragment, or organic remnant that is produced by mechanical weathering and bcomes part of a clastic sediment or rock
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
the breaking of a mineral along a set of parallel identical atomic planes
a two-dimensional lattice characterized by two translations of different magnitudes at nonspecial angles to each other
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
appearing as spherical or hemispherical shpaes made of radiating crystals (see also globular)
a sensation produced by different wavelengths of light hitting the eye
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
a term describing fracturing that produces curvged surfaces similar to when glass breaks; for example, quartz has a conchoidal fracture
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...
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
a term describing a material containing generally submicroscopic grains whose crystalline nature is not easily determined
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.
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
a closed form of six identical square faces of 90degree to each other
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
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
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
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
the distance betwen adjacent planes with the same Miller indices
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
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
a term describing an aggregate of crystals having a treelike appearance (see also arborescent)
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
referring to a product of mechanical weathering
detrital sedimentary rock
rock formed by lithification of detrital sediments
broken-up material resulting from mechanical weathering
chemical, physical, and biological changes that affect sediment or sedimnetary rocks after initial deposition, but excluding weathering or metamorphism
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
the ability of a mineral to transmit light; often described as transparent, translucent, or opaque
an adjustable opening used to control the size of a light beam in a polarzing light microscope
pleochroism of a mineral that is observed as two different colors
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
an instrument that recods x-ray diffraction patters
describing a layered mineral structure in which only two or three available octahedral sites are occupied
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
a closed cubic form of 24 quadrilateral faces; a from of crystal class 2/m3
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
a difference in wave velocity for different wave lengths
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
the process of dissolving
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
a closed cubic form of 12 faces that may have any of a number of shapes and point group symmetries
a chemical sedimentary rock composed primarily of dolomite
a region within a crystal having a structure or orientation that differs from other regions within the crystal
an open crystal form composed of two nonparallel faces related by a mirror
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
having surfaces coated with fine crystals
a term used to describe the tenacity of mienrals that are capable of being drawn into a wirelike shape
a type of luster that does not reflect significant amounts of light or show any play of colors
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)
see extraordinary ray
eclogite (facies)
a high-pressure/high-temperature metamorphic facies characteristic of the mantle
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
a bubbling reacton; the term used to describe the reaction of calcite with dilute hydrochloric ace
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
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
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
a basic chemical unit composed of atoms having the same atomic number; elements cannot be separated into simpler parts by chemical means
a term describing crystals that are very small ellipsoids
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
a thermodynamic variable related to the Gibbs free energy
a thermodynamic variable representing the degree of randomness or disorger in a system
refers to a mineral deposit that is emplaced after its host rock already exists

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