Mineralogy Terms

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accessory mineral

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a mineral present in small amounts in a rock, unimportant for rock naming or classification

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accesssory plate

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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.

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Acicular

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having a needle like shape

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actinide

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elements (such as Th, Pa, and U) with atomic numbers 90 through 103 and valence electrons in 5f orbitals

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acute bisectrix

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aline bisecting the angle formed by the two optic axes in a biaxial mineral

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acute bisectrix figure (Bxa)

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the interference figure seen when looking down an acute bisectrix

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adamantine

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a type of luster that is bright, sparkly, and shiny similary to that of diamonds

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aggregate (or crystals)

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a mass of crystals, of the same or different minerals, that may be physically separated, perhaps with some difficulty

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albite twin

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a common twin law in ticlinic feldspars, often resulting in polysynthetic twins

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alchemy

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chemistry of the Middle Ages that combind science, magic, and philosophy

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alkali element

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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

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Alkaline earth element

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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

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allochromatic

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a term descriving a mineral that gets its color from minor or trace elements (see also iodiochromatic)

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alloy

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a noncrystalline mixture of two or more metals

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alluvium

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unconsolidated sediment deposited by a stream

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amorphous

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having a random atomic structure (see also noncrystalline)

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amphibolite (facies)

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one of the principal metamorphic facies introduced by Eskola, corresponding to high-grade conditions of about 450 - 650 and 3- 8 Kbar

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amphibolite (rock)

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a metamorphic rock containing primarily hornblende and plagioclase

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analyser

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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)

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anatexis

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melting of preexisting rock

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andesite

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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

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angle of incidence

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the angle that an impinging ray makes with a normal to an interface

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angle of refraction

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the angle that a refracted ray makes wit ha normal to an interface

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anhedral

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a crystal that lacks well-developed crystals faces or that has rounded or irregular form due to crowding by adjacent crystals

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anion

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an ion having a negative charge

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anionic complex

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a tightly bonded, negatively charged moleculr group; in mineral formulas, often surrounded by parentheses

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anisodesmic

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describing an ionic compound in which the ionic bonds are not all of the same strength

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anisotropic

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having different physical properties in different directions

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anomalous interference colors

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interference colors that are not represented on the Michel Levy Chart; typically associated with minerals of exteremely low birefringence, such as chlorite

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aphanitic

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having no mineral grains that are visible to the naked eye

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aqueous solution

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a water-rich solution, usually containing dissolved elements or complexes

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arborescent

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a term descrving an aggregate of crystals having a treelike appearance (see also dendritic)

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arenite

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

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arkose

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a feldsapr-rich sandstone

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asbestiform

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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

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asbestos

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a genral term referring to minerals that have an asbestiform habitl chrysotile, amosite, and crocidolite are typical asbestos minerals

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association (mineral)

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a group of minerals found together in a rock

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asterism

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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

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atmophile

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an element that tends to concentrate in the Earth's atmosphere

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atomic absorption spectrophotometer

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an analytical instrument in which compoistion is determind by measuring the absorption of characterisitc wavelengths of light by an atomized and flamed sample

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atomic mass unit (amu)

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unit for expressing atomic mass, equal to approximately 1.66x10^-24 grams

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atomic number(Z)

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the number of protons in the nucleus of an atom of an element

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atomic weight

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the weight of an atom or compound in atomic mass unitsl generally close to the total number of protons and neutrons

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Aufbaur principle

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the principle that states that electrons fill orbitals in a systematic way from the lowest energy orbitals to the highest

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augen

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lagrge lenticular mineral grains or mineral aggregates in a foliated metamorphic rock

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augen gneiss

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a gneiss containing augen

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authigenic

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formed or generated in place; used to describe minerals that form in a sediment or sedimentary rock after deposition of an original sediment

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Avogadro's number

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6.022x10^23, equivalent to the number of atoms or molecules in a mole

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Axial ratio

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the ration of unit cell lengths along each crystallographic axis, a:b:c

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axis (crystallographic)

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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

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axis (rotational)

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a symmetry element that relate identical crystals faces or other things by rotation of 60, 90, 120, 180, or 360 about an axis

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Banded iron formation(BIF)

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a layered rock containing chert, silicate, carbonate, or oxide layers, giving a banded appearence

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Basal cleavage

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a term used to describe the cleavage in minerals such as micas that allows the ineral to break into plates or sheets

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Basalt

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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)

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basement (rock)

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metamorphic and igneous rocks that underlie sediments and sedimentary rocks observed at the Earth's surface; often, though not exclusively, of Precambrian age

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basis

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a sufficient set of symmetry operators for descriving the symmetry of crystals (translation-free symmetry) or of atomic structures (space sysmmetry)

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bauxite

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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

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Baveno twin

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an uncomomon twin law in feldspar

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Becke line

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

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bentonite

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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

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Berman blaance

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a type of balance scale used to determine specific gravity

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Betrand lens

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a lends that can be inserted in the tube of a polarizing light microscope to facilitate observation of interference figures

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biaxial

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describing a crystal having two optic axes and three principal indices of refraction. Such crystals belong to the orthorhombic, monoclinic, and triclinic crystal systems

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binary solution

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a solid solution series that can be characterized by two end members

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birefringence (property)

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the property of a crystal that causes double refraction

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birefringence (value)

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the difference between the greatest and least indices of refraction

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bladed

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having the appearance of blades

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blocky

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a term used to describe crystals that have a blocklike appearance, generally with an approximately square cross section

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blueschist (facies)

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one of the principal metamorphic facies introduced by Eskola, corresponding to high pressure-low temperature conditions

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blueschist (rock)

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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.

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body centered

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said of a unit cell that has an extra lattice point at its center

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body diagonal

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aline passing through the center of a cube or other three-dimensional geometric shape and connecting opposite corners

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Bohr model of the atom

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a fundamental model of an atom that states that electrons orbit atomic nuclei in orbits associated with specific energy levels

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bomb

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a laboratory reactor vessel used to synthesize gems and minerals at high pressure and temperature

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bort

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dimond of low quality that is unsuitable as a gem but useful in industrial applications

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botryoidal

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a term used to describe a mineral habit that appears like a bunch of grapes

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boule

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a oblong-shaped synthetic mineral crystal that is produced from the Verneuil technique

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Bowen's reaction series

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a hypothetical series that describes the order of crystallization of minerals from magma

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Bragg law

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a mathematical law that describes the relationship between the angle of diffraction, x-ray wavelength, and atomic plane spacing

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Bravais lattices

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the fourteen possible three-dimensional lattices that can describe mineral structures

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Brazil twin

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a common type of twinning in quartz

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Breccia

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a clastic sedimentary rock composed of large angular broken rock fragments in a finer grained matrix

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Bridging oxygen

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

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brittle

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a term used to describe minerals that shatter or break easily when struck

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brucite layer

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a sheet of Mg(OH)6 octahedra in a layered crystal structure

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Buerger precession camera

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an instrument designed to record single crystal diffraction patterns on film

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burial metmorphism

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metamorphism affecting a large region; caused by pressure related to depth in the Earth and temperature related to geothermal gradient (see also regional metamorphism)

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Cabochon

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a gemstone that has been ground and polished into a domed shape

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calcine

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the heat material, such as limestone, to high temerature, breaking down minerals and driving off carbon dioxide or other volatiles

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capillary

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having a hairlike or threadlike appearance (see also filiform)

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carbonate (mineral)

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a group of minerals with formulas characterized by (CO3) 2- radicals

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Carbonate (radical)

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the (CO3) 2- anionic group

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Carbonate (rock)

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a chemical sedimentary rock dominated by carbonate minerals; limestone or dolostone

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Carbonation reaction

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reaction of a mineral or minerals with CO2 to produce a product carbonate mineral

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Carlsbad twin

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a commmon twin law in orthoclase, less common in other feldspars, often resulting in penetration twins

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Cartesian coordinate system

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an X-Y-Z coordinate system in which all axes are at 90degree and the unit distances along all axes are equal

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Cataclastic metamorphism

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metamorphism caused by a transient high-pressure condition such as a meteor impact (see also shock metamorphism and dynamic metamorphism)

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Cathode ray tube

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Vacuum tube in which beams of high-energy electrons pass through magnetic fields and hit a fluorescent screen

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cation

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an ion having a positive charge

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cementation

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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

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centered

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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..

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chain silicates

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silicate minerals characterized by SiO4 tetrahedra joining to form chains either one tetrahedron or two tetrahedra wide (see also inosilicates)

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chalcophile

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an element that tends to concentrate in sulfide minerals and ores

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characteristic radiation

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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

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chatoyancy

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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

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chemical precipitate

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a solid that precipitates from an aqueous solution, typically due to supersaturation

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chemical sedimentary rock

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a sedimenatray rock composed primarily of material formed by precipiation from solution; for example, most limestones and all evaporites

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chemical sediments

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

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chemical weathering

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type of weathering involving chemical reactions that transform or decompose miinerals and rock

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chert

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a hard sedimentary rock composed primarily of cryptocrystalline silica, generally in the from of cibrous chalcedony with lesser amounts of quartz and opal

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chromophores

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elements that give minerals their color

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clast

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a mienral grain, lithic fragment, or organic remnant that is produced by mechanical weathering and bcomes part of a clastic sediment or rock

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clastic

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being composed of grafments (clasts) derived from preexisting rocks

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clastic rock

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sedimentray rock formed by the lithification of clsatic sediments; for example, sandstone, shale, and siltstone

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Clausius-Clapeyron equation

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an equation relating the slope of a reaction on a prssure-temperature diagram to the entropy volume change of the reaction

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clay (grain size)

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a clastic fragment of any cmposition smaller than silt, having a dimaeter less that 1/256 mm

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clay (mineral)

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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

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cleavage

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the breaking of a mineral along a set of parallel identical atomic planes

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clinonet

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a two-dimensional lattice characterized by two translations of different magnitudes at nonspecial angles to each other

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clinopyroxene

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monoclinic pyroxene subgroup dominated by end members diopside and hedenbergite. The most common of all pyroxenes

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closet packing

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the most effecient way to pack like atoms together in three dimensions; each atom is surrounded by 12 others