Mineralogy Terms

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accessory mineral

Back 1

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

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accesssory plate

Back 2

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

Back 10

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

Back 14

a noncrystalline mixture of two or more metals

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alluvium

Back 15

unconsolidated sediment deposited by a stream

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amorphous

Back 16

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

Back 20

melting of preexisting rock

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andesite

Back 21

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

Back 121

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

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colloform

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appearing as spherical or hemispherical shpaes made of radiating crystals (see also globular)

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color

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a sensation produced by different wavelengths of light hitting the eye

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columnar

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having the appearance of an aggregate of slender, elongated individual crystals, nearly parallel in arrangement

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complex twin

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a twin composed of more than two individual crystals

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compositional zoning

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variation in the composition of a crysta, typically from core to margin (see also zoning)

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compound (chemical)

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a substance of fixed atomic proportions made by the combination of two or more elements

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concentration fact

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the extent to which an element must be concentrated above normal crustal levels to make minig it profitable

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conchoidal

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a term describing fracturing that produces curvged surfaces similar to when glass breaks; for example, quartz has a conchoidal fracture

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condenser

Back 130

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)

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condensive lens

Back 131

see condenser...

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conglomerate

Back 132

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

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conoscopic illumination

Back 133

describing the strongly convergent light produced by the insertion of a condensing lens in a polarizing light microscope substage

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constructive interference

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the addition of two waves that are in phase with negligible or no loss of energy

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contact aureole

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a contact metamorphic zone surrounding an igneous intrusion (see also aureole)

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contact metamorphism

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metamorphism localized around an igneous rock body; primarily in response to heat and flowing fluids.

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Contact twin

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a twin in which two individuals are symmetrically arranged about a twin plane

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Continuous radiation

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the low-intensity radiation covering a range of wavelengths , produced by and X-ray tube; continuous radiation provides the background for characteristic radiation

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continuous side (Bowen's reaction series)

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the side of Bowen's reaction series characterized by plagioclase

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coordinating polyhedron

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polyhedron formed around an atom or ion by ocnnecting the centers of the coordinated atoms or ions

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coordination number

Back 141

number of neighboring atoms to which and atom is bonded

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country rock

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rock intruded by and surrounding an igneous intrusion

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coupled substitution

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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

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covalent bond

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an ideal chemical bond that involves the sharing or orbital electrons between elements that have little or no difference in electronegativity

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cover slip

Back 145

a thin piece of glass that is placed over grains and liquid to make a grain mount

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critical angle

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the angle of incidence that yields an angle of refraction of 90 degrees

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crossed polars

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the condition caused when the upper polarizer is inserted in a polarizing light microscope

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cryptocrystalline

Back 148

a term describing a material containing generally submicroscopic grains whose crystalline nature is not easily determined

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crystal

Back 149

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

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crystal classes

Back 150

the 32 possible combinations of symmetry elements that a crystal may have; in modern usage, practically synony mous with the 32 possible point groups

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crystal morpholofy

Back 151

the shape and form(s) of a crysral

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crystal structure

Back 152

spatial arrangement of atoms or ions, and their bonds in a crystal

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crystal structure determination

Back 153

determination of the spatial arrangement of atoms and their bonds in a crystal

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crystal system

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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.

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crystalline

Back 155

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

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crystallographic axis

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a direction corresponding to one of the three edges of a chosen unit cell in a crystal lattice

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cube

Back 157

a closed form of six identical square faces of 90degree to each other

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cubic

Back 158

having a cube shape or belonging to the cubic system

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cubic (coordination)

Back 159

the bonding of an ion to eight others arranged so that connecting their centers forms a cube

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cubic (system)

Back 160

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

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cubic closest packing

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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

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cumulate

Back 162

a layer of minerals accumulated by gravity settling of crystals as they form in a magma chamber

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cyanide method

Back 163

a method for extracting valuable metals from ore that involves hydrogen cyanide

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cyanide method

Back 164

a method for extracting valuable metal ore that involves hydrogen cyanide

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cycle

Back 165

one complete upward and downward motion by a wave

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cyclic twinning

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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

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cyclosilicates

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silicate minerals characterized by SiO4 tetrahedra joining to from rings (see also ring silcates)

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Czochralski process

Back 168

a method of making synthetic gems that involves a seed crystal drawing materals out of a melt

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d-value

Back 169

the distance betwen adjacent planes with the same Miller indices

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dacite

Back 170

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

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daughter element

Back 171

the product element of radioactive decay

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daughter isotope

Back 172

the product isotope of radioactive decay

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Dauphine twin

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a common type of twinning in quartz

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Debeye-Scherrer camera

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the most commonly used and most versatile camera for obtaining powder diffraction patterns

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decarbonation reaction

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a reaction that liberates CO2 from a mineral

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defect

Back 176

a flaw in an otherwise ideal crystal structure

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degrees of freedom

Back 177

the number of intensive variables that may be changed independently without causing a change in mineral assemblage or composition

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dehydration reaction

Back 178

a reaction that liberates H2O from a carbonate mineral

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dendritic

Back 179

a term describing an aggregate of crystals having a treelike appearance (see also arborescent)

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density

Back 180

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

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destructive interference

Back 181

the addition of two out-of-phase waves resulting in a total, or significant, loss of energy

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detrital

Back 182

referring to a product of mechanical weathering

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detrital sedimentary rock

Back 183

rock formed by lithification of detrital sediments

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detritus

Back 184

broken-up material resulting from mechanical weathering

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detrital sedimentary rock

Back 185

rock formed by lithification of detrital sediments

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detritus

Back 186

broken-up material resulting from mechanical weathering

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diagenesis

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chemical, physical, and biological changes that affect sediment or sedimnetary rocks after initial deposition, but excluding weathering or metamorphism

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diamagnetism

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a property of minerals that causes a small negative reaction (repulsion) to a magnet

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diamond (shape)

Back 189

a parallelogram having four sides of equal length and no angles at 90 degrees

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diamond lattice

Back 190

see diamond net

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diamond net

Back 191

a two-dimensional lattice characterized by two translations of the same magntude at nospecial angles to each other

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disphaneity

Back 192

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

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diaphragm

Back 193

an adjustable opening used to control the size of a light beam in a polarzing light microscope

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dichroism

Back 194

pleochroism of a mineral that is observed as two different colors

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diffraction

Back 195

apparent bending of radiation by evenly spaced atoms, slits, or gratings

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diffraction grating

Back 196

a grating that causes diffraction

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diffraction slit

Back 197

a slit that causes diffraction

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diffractometer

Back 198

an instrument that recods x-ray diffraction patters

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dioctehedral

Back 199

describing a layered mineral structure in which only two or three available octahedral sites are occupied

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diorite

Back 200

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

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diploid

Back 201

a closed cubic form of 24 quadrilateral faces; a from of crystal class 2/m3

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dipyramid

Back 202

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

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discontinuous side (Bowen's reaction series)

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the side of Bowen's reaction series characterized by olivine-pyroxene-anphibole-biotite

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disequilibrium

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dispersion

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dispersion

Back 205

a difference in wave velocity for different wave lengths

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disphenoid

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a closed crystal form comprising two sphenoids related by 222 symmetry

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disseminated deposit

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an ore deposit in which the ore mineral is scattered throughout a host rock

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dissolution

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the process of dissolving

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divalent

Back 209

having a charge of -/+ 2

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divariant field

Back 210

a region on a phase diagram characterized by two degrees of freedom

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divergent (crystals)

Back 211

slender crystals emanating from a common point (see also radiating)

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dodecahedral (coordination)

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12-fold coordination

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dodecahedron

Back 213

a closed cubic form of 12 faces that may have any of a number of shapes and point group symmetries

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dolostone

Back 214

a chemical sedimentary rock composed primarily of dolomite

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domain

Back 215

a region within a crystal having a structure or orientation that differs from other regions within the crystal

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dome

Back 216

an open crystal form composed of two nonparallel faces related by a mirror

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dop

Back 217

a sticklike device that holds a gem crystal for grinding on a wheel

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double chain silicates

Back 218

silicate minerals characterzied by SiO4 tetrahedra joining to form chains two tetrahedra wide (see also amphibole)

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double refraction

Back 219

the ability of a mineral to split ordinary light into two waves of different velocities and polarization

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doubly primitive

Back 220

term describing a unit cell containing a total of two lattice points

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drusy

Back 221

having surfaces coated with fine crystals

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ductile

Back 222

a term used to describe the tenacity of mienrals that are capable of being drawn into a wirelike shape

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dull

Back 223

a type of luster that does not reflect significant amounts of light or show any play of colors

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dunite

Back 224

an ultramafic intrusive rock in which the only major mineral is olivine; chromite is typicall ypresent as an accessory mineral

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dynamic metamorphism

Back 225

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

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E-ray

Back 226

see extraordinary ray

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eclogite (facies)

Back 227

a high-pressure/high-temperature metamorphic facies characteristic of the mantle

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eclogite(rock)

Back 228

a high pressure/high-temperature rock containing Mg-rich garnet (pyrope) and Na-rich clinopyroxene (omphacite); mostly of mantle origin

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edge diagonal

Back 229

a line passing through the center of a cube or other three-dimensional geometirc shape, and connecting the centers of opposite edges

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edge dislocation

Back 230

a kind of line defect caused by a terminated roc of atoms

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edge sharing

Back 231

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

Front 232

effective ionic radius

Back 232

radius of a spherical volume effectively occupied by an ion in a particular structure

Front 233

effervescence

Back 233

a bubbling reacton; the term used to describe the reaction of calcite with dilute hydrochloric ace

Front 234

elastic

Back 234

a term used to describe mienrals that return to their original shpae after bending

Front 235

electromagnetic radiation

Back 235

emission or transfer of energy in the form of waves; includes x-rays, visible light, infrared light, radiowaves, and television waves

Front 236

electron

Back 236

an extremely small atomic particle having little mass and the smallest negative electric charge occurring in nature. Atoms have electrons orbiting around a nucleus.

Front 237

electron cloud

Back 237

the space occupied by electrons surrounding an atomic nucleus

Front 238

electron cloud

Back 238

the space occupied by electrons surrounding an atomic nucleus

Front 239

electron microprobe

Back 239

an analytical instrument in which a finely focused electron beam hits a sample, causing emission of elemental characterisitc radiation

Front 240

electronegativity

Back 240

measure of the tendency of elements to acquire electrons

Front 241

electrostatic valency principle (Pauling's rule 2)

Back 241

the strength of an ionic bond is equal to its ionic charge divided by its coordination number

Front 242

element

Back 242

a basic chemical unit composed of atoms having the same atomic number; elements cannot be separated into simpler parts by chemical means

Front 243

elliptic

Back 243

a term describing crystals that are very small ellipsoids

Front 244

enantiomorphic

Back 244

a term describing two crystals whose atomic structues are mirror images of each other

Front 245

end centered

Back 245

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

Front 246

end member

Back 246

an ideal chemical formula representing one limit of a solid solution

Front 247

energy level

Back 247

the enrgy associated with a particular electron orbit in an atom

Front 248

enthalpy

Back 248

a thermodynamic variable related to the Gibbs free energy

Front 249

entropy

Back 249

a thermodynamic variable representing the degree of randomness or disorger in a system

Front 250

epigenetic

Back 250

refers to a mineral deposit that is emplaced after its host rock already exists

Front 251

equant

Back 251

having approximately the same dimensions in all directions

Front 252

equilibrium

Back 252

a static state of a chemical system in which the relative amounts and compositions of phases present do not undergo changes with time

Front 253

essential mineral

Back 253

a ineral in a rock that is necessary for the rock to be classified or named as it is

Front 254

euhedral

Back 254

a crystal that is completely bounded by well-developed crystal faces and whose growth was not restrained by adjacent crystals

Front 255

evaporite (mineral)

Back 255

minerals that may form by precipitation from aqueous solutiom under norma Earth surface conditions; for example massive gypsum or salt beds

Front 256

evaporite (mineral)

Back 256

minerals that may form by precipitation form aqueous solution under normal Earth surface conditions; for example halite, sylvite, and gypsom

Front 257

evaporite (rock)

Back 257

a chemical sedimentary rock formed by evaporation of water; for example massize gypsum or salt beds

Front 258

evaporite deposit

Back 258

mienral deposit formed by evaporation of water

Front 259

even (fracture)

Back 259

a fracutre that produces smooth planar surfaces

Front 260

exhalitive

Back 260

a hydrothermal deposit created at the Earth's surface; generally one that forms on the ocean floor from springs

Front 261

expandable clay

Back 261

one of a group of clay minerals (smectites) that can exdpand their structure to accommodate excess water or other chemical components

Front 262

exsolution

Back 262

the separating of an initially homogeneous mineral solid solution into two (or more) zones of distinct mineral phases; for example, the formation of perthit from an homogenous feldspar during cooling

Front 263

exsolution lamellae

Back 263

fine parallel zones of different compositions resulting from exsolution

Front 264

extinct (mineral grain)

Back 264

a term describing a birefringent mienral grain oriented so that it appears dark when viewed under crossed polars

Front 265

extinct (x-ray peak)

Back 265

a term describing an x-ray peak missing from a diffraction pattern due to destuctive interference

Front 266

extinction

Back 266

the systematic absence of a related group of x-ray peaks in a diffraction pattern

Front 267

extinction angle

Back 267

the angle, measured under crossed polars, between the position of extinction and a cleavage, long dimenision, or other direction in a crystal

Front 268

extraordinary ray

Back 268

in a uniaxial crystal, the ray of light that vibrates in a plane containing the optic axis

Front 269

extrusive rock

Back 269

an igneous rock that crystallizes at or very near the Earth's surface (see also volcanic rock)

Front 270

face centered

Back 270

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

Front 271

face sharing

Back 271

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

Front 272

facet

Back 272

a polished face on a gemstone

Front 273

facies (metamorphic)

Back 273

a range of pressure-temperature conditions characterized by one or more specific mineral assemblages

Front 274

family of planes

Back 274

an infinite number of planes, parallel and spaced equally, all characterized by one or more specific mineral assemblages

Front 275

fast ray

Back 275

the fastest of two rays produced by double refraction

Front 276

feldspathic

Back 276

an adjective describing a mineral aggregate containing feldspar

Front 277

felsic

Back 277

a general adjective referring to igneous rocks having light colored minerals in their mode

Front 278

feroomagnetism

Back 278

a type of magnetic order, characteristic of iron, that causes a mineral to respond strongly to a magnetic field

Front 279

fibrous (cleavage)

Back 279

a term describing a cleavage that allows crystal to be broken into fibers

Front 280

fibrous (crystals)

Back 280

having the appearance of being composed of fibers

Front 281

filiform

Back 281

having a hairlike or threadlike appearance (see also capillary)

Front 282

fissility

Back 282

the rock property of breaking easily along closely spaced planes; often used to describe shale or schist

Front 283

flash figure

Back 283

the interference figure observed when the optic axis (uniaxial mineral) or the optic plane (biaxial minera) are oriented parallel to the stage of polarizing light microscope

Front 284

flexible

Back 284

a term used to describe the tenacit yof mineral that are bendable

Front 285

flood basalt

Back 285

a laterally extensive and thick lava flow of basaltic composition

Front 286

fluorescence

Back 286

a type of luminescence that occurs when minerals are exposed to ultraviolet light, xrays, or cathode rays, but ceases when the exposure ceases

Front 287

flux

Back 287

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

Front 288

flux method

Back 288

a method of synthesizing gems or other mienrals by growing them in an inert flux

Front 289

foliated

Back 289

having planar or sheetlike properties

Front 290

foliation

Back 290

a planar fabric or texture

Front 291

fool's gold

Back 291

common name foor pyrite

Front 292

form

Back 292

a set of identically shpaed crystal faces related by symmetry

Front 293

fractional crystallization

Back 293

separation of a crystallizing magma into parts by the successive crystallization of different minerals (see also partial crystallization)

Front 294

fracture

Back 294

breaking of a mienral other than along planes of cleavage

Front 295

framework silicates

Back 295

silicate minerals characterized by SiO4 tetrahedra joining to form three-dimensional networks (see also tectosilicates and network silicates)

Front 296

Frenkel defect

Back 296

a defect caused when an atom in a crystal structure is displaced from its normal position to a different position

Front 297

gabbro

Back 297

an intusive igneous rock of mafic composition containing plagioclase as the only major feldspar; clinopyroxene +/- orthopyroxene +/- olivine are typically present (see also basalt)

Front 298

gamma rays

Back 298

electromagnetic radiation of higher energy and shorter wavelength than X rays; emitted by atomic nuclei

Front 299

gangue

Back 299

the waste minerals in an ore deposit

Front 300

gem

Back 300

an especialy fine or superlative specimen, often 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

Front 301

gemmy

Back 301

having a gemlike appearance; typically having a bright color, an attractive luster, or geometric shape

Front 302

gemstone

Back 302

a gem of mineralogical origin

Front 303

general angle

Back 303

a nonspecial angle between crystal faces or symmetry elements

Front 304

general form

Back 304

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

Front 305

general point

Back 305

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

Front 306

geode

Back 306

a hollow or partly hollow rock cavity lined by mineral material

Front 307

geothermometer

Back 307

a mineral or mineral sstem with compositional variations that reflect the temperature at which it formed

Front 308

Gibbs free energy

Back 308

a termodynamic variable that describes the relative stability of a mineral or a mineral assemblage; also refers to the energy change associated with a chemical reaction

Front 309

Gibbs phase rule

Back 309

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

Front 310

gibbsite layer

Back 310

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

Front 311

glass

Back 311

an amorphous solid material; in most cases, a metastable supercooled liquid

Front 312

glide plane

Back 312

a compound symmetry operation that repeats a motif or other entity after a reflection

Front 313

glide plane

Back 313

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

Front 314

globular

Back 314

appearing as spherical or hemispherical shapes made of radiating crystals (see also colloform)

Front 315

gneiss

Back 315

a foliated metamorphic rock showing contrasting bands of light- and dark-colored minerals

Front 316

Goldich's weathering series

Back 316

a hypothetical serires that describes the order of wetahering of mineral in outcrop; the series is essentially the opposite of Bowen's reaction series

Front 317

goniometer

Back 317

a calibrated instrument used to measure the angles btween crystal faces, cleavages, or other planar features in crystals. Simple goniometers consist of a protractor attached to a rotatable ruler

Front 318

grade (metamorphic)

Back 318

the degree of metmorphism; generally equivalent to the temperature of metamorphism (see also metamorphic grade)

Front 319

grade (ore)

Back 319

the concentration of ore minerals or elements in ore rock

Front 320

grain mount

Back 320

mineral grains on a glass slide surrounded by a liquid and covered with a cover slip

Front 321

granite

Back 321

an intrusive igneous rock of silicic composition containing10% to 50% quartz and K-feldsapr as the major feldspar; plagioclase, biotie, and hornblende may be present (see also rhyolite)

Front 322

granitic

Back 322

a general adjective applied to any light-colored intrusive igenous rock or to any rock composition that generally resembles that of a granite

Front 323

granodiorite

Back 323

an intrusive igneous rock of silicic composition that contains more plagioclase than K-feldspar, biotite and hornblende are typicall present (see also dacite)

Front 324

granular

Back 324

cojmposed of many small grains

Front 325

granulite (facies)

Back 325

the metamorphic facies corresponding to the highest grades of regional metamorphism

Front 326

granulite (Rock)

Back 326

a high-grade metamorphic rock containing orthopyroxene

Front 327

gravel

Back 327

clastic materal with grains greater that 2 mm in diameter, may include boulders, cobbles, pebbles, or granules

Front 328

graywacke

Back 328

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

Front 329

greasy

Back 329

a type of luster describing crystal faces or other surfaces that reflect light and give of play of colors similar to oil on water

Front 330

greenschist

Back 330

a medium-grade metamorphc rock characterized by schistosity and green mienrals including actinolite, chlorite, and epidote

Front 331

greenschist (facies)

Back 331

a medium-grade metamorpich facies characterizing conditions of about 300-500 C and 2-8 Kbar

Front 332

greenstone

Back 332

a vague term used to describe any fine-grained low-grade green metamorphic rock; generally of basaltic composition

Front 333

greenstone belt

Back 333

a metamorphic terrane characterized by the presence of low-grade metamorposed volcanics and volcanogenic sediments and silicic to intermediate plutons

Front 334

group (of elements)

Back 334

the elements of one column in the Periodic Table of the elements

Front 335

group (of minerals)

Back 335

minerals within a class or subclass that share major chemical or structural features

Front 336

gypsum plate

Back 336

a accessory plate, made of gypsoum, for a polarizing light microscope

Front 337

gyroid

Back 337

a cubic form of 24 irregular pentagonal faces; a form of crystal class 432

Front 338

habit

Back 338

the characteristic appearance of a mineral due to crystal form or combinations of forms, crystal intergrowths, and aggreagates and any other irrefular physical characteristics

Front 339

hackly

Back 339

a term describing fracturing that produces jagged edges

Front 340

halide

Back 340

mineral compound characterized by a halogen such as F, Cl, or I as an anion

Front 341

halogen

Back 341

elements (such as F, Cl, and Br) in the seventeenth group of the periodic table of the elements; halogens typically ionize to become monovalent anions

Front 342

Hanawalt method

Back 342

a systematic method for matching an "unknown" x-ray pattern with one in a reference data set such as the Powder Diffraction File

Front 343

hand specimen

Back 343

a piece of rock or mineral convenient for studying macroscopic properites, that can be picked up in the hand

Front 344

hard radiation

Back 344

x rays of extremely high energy; used in industry and manufacturing but generally not by crystallographers

Front 345

hardness

Back 345

the resistance of a mineral to scratching

Front 346

Haiiy's Law

Back 346

a law that states that crystal faces make simple rational intercepts with crystallographic axes; a corrolary is that crystal faces have rational and general small Miller indcies (see also Law of Rational indices)

Front 347

heavy liquid

Back 347

a liquid of greater density than water that may be used to separate minerals of different densities

Front 348

heft

Back 348

an estimation of a minera's density obtained by picking up the mineral and holding in your hand

Front 349

Heisenberg uncertainty principle

Back 349

a principle stated by Werner Heisenberg that says it is impossible to know the location and motion of an electron in an atom without some uncertainty

Front 350

Hermann-Mauguin symbol

Back 350

a shorthand notation for the symmetry of a point group

Front 351

hexhonal

Back 351

of or a related to the hexgonal system

Front 352

hexagonal (system)

Back 352

a crystal system characterized by lattice symmetry 6/m2/m2/m, and containing point groups with symmetry no greater than 6/m2/m2/m; two cell parameters (a,c) are needed to describe the shape and size of a hexagonal unit cell

Front 353

hexagonal closet packing

Back 353

closest packing of spheres in an orrangement similar to a hexgonal prism with three extra spheres in its interior; equivalent to stacking closest packed layers in an ABABAB sequence

Front 354

hexagonal packing

Back 354

packing of identical spheres in a plane so that each is surrounded by six others

Front 355

hexhedron

Back 355

a form of six equivalent faces related by symmetry; for example, a cube or rhombohedron

Front 356

hexanet

Back 356

a two-dimensional lattice characterized by two tranlations of equal magnitude of 60degrees to each other

Front 357

hexoctahdron

Back 357

a cubic form of 48 triangular facesl a form of crystal class 4/m32/m

Front 358

hornfels

Back 358

a fine-grained metamorphic rock lacking foliation or lineation

Front 359

host rock

Back 359

the rock tht hosts ore minerals or an ore deposit

Front 360

hydration reaction

Back 360

a reaction between minerals, or minerals, and water that results in a product hydrous mineral

Front 361

hydrogen bond

Back 361

a type of electrostatic bond that is generally insignificant in minerals. Prominent in ice and, to a lesser extent, in micas and hydroxides

Front 362

hydrolyaste

Back 362

the material that goes into solution during chemical weatherin

Front 363

hydrolysis reaction

Back 363

a type of weathering reaction that simultaneously produces dissolved material and secondary minerals

Front 364

hydrothermal

Back 364

having to do with warm water-rich fluids

Front 365

hydrothermal fluids

Back 365

hot water-rich fluids that circulate through the Earth

Front 366

hydrothermal ore deposit

Back 366

an ore deposit precipitated by hydrothermal fluids

Front 367

hydroxide

Back 367

a chemical group, or group of minerals, with formulas characterized by the radical (OH)-; for example, gibbsite, Al(OH)3

Front 368

hypothesis

Back 368

a propsoed explanation for an observed set of facts

Front 369

idiochromatic

Back 369

term describing a mineral that gets its color from its major elements (see also allochromatic)

Front 370

igneous

Back 370

an adjective describing a rock or mineral that solidified form a magma or describing the process that forms such a rock or mineral

Front 371

immersion method

Back 371

a method for determining index of refraction by ommersing a grain in liquid or known index of refraction

Front 372

immiscibility

Back 372

an inability of tow or more phases to dissolve completely in one another

Front 373

impurity defect

Back 373

a defect caused when a foreign atom is present in a crystal structre

Front 374

inclined extinction

Back 374

extinction when a principal cleavage or length of a crystal is at an angle to the crosshairs of a polarizing light microscope

Front 375

incompatible element

Back 375

an element that does not readily enter a crystal structure

Front 376

index (indices)

Back 376

number (numbers) used to describe the location of points, the riention of line, or the orientation of planes in space

Front 377

index (x-ray pattern)

Back 377

to assign appropriate (hkl) vlaues to x-ray diffraction peaks

Front 378

index mineal

Back 378

a mineral characteristic of a particular set of pressure-temperature conditions for rocks of a given composition

Front 379

index of refraction

Back 379

the ration of the velocity of light in a vacuum to the velocity of light in a crystal, glass, liquid, or other medium (see also refractive index(

Front 380

inert gas

Back 380

any of the generally unreactive elements (such as Ne, Ar, or Kr) in the eighteenth group of the PEriodic Table of the Elements (see also noble gas)

Front 381

infrared light

Back 381

electromagnetic radiation with wavelengths slightly greater than visible light

Front 382

inorganic

Back 382

a general term used to refer to compounds that contain no carbon bonded to hydrogen as essential components

Front 383

inosilicates

Back 383

chain silicates; either pyroxenes, pyroxenoids, or amphiboles

Front 384

integral molecules

Back 384

the fundamental and indivisible building blocks making up crystals, according to Ha,y: now known not to exist as Ha,y envisioned them

Front 385

intensive variable

Back 385

a termodynamic variable, genrally pressure or temperature, that is controlled from outside a chemical system

Front 386

interfacial angel

Back 386

the angle between two faces of a crystal

Front 387

interference

Back 387

the interaction of two waves traveling in the same direction

Front 388

interference colors

Back 388

the colors displayed by a birefringent crystal when viewed under crossed polars

Front 389

intergranular fluid

Back 389

a fluid between grains in a rock

Front 390

intergrowth

Back 390

two or more crystals grown together

Front 391

intermediate igenous rock

Back 391

an igneous rock of composition intermediate between mafic and silicic

Front 392

internal energy

Back 392

a thermodynamic variable related to Gibbs free energy

Front 393

internal reflection

Back 393

the reflection of a light ray back into the interior of a crystal when it reaches a crystal boundary from within

Front 394

interstice

Back 394

a space between grains in a rock or between closest packed atoms in a structure

Front 395

intrusive rock

Back 395

an igneous rock that crystallizes at depth in the earth (see also plutonic rock)

Front 396

invariant point

Back 396

a point on a phase diagram at which two or more reactions intersect

Front 397

inversion

Back 397

a term describing the operation that relates two crystal faces or other entities that are equal distant from a central point and have upside-down and backward orientations with respect to each other

Front 398

inversion center

Back 398

a point at the center of a crystal (and its atomic structure) through which every aspect of the crystal (and its atomic sructure) is repeated by inversion

Front 399

ion

Back 399

an atom with a negative or positive electric charge as a result of having lost or gained one or more electrons

Front 400

ionic bond

Back 400

an ideal chemical bond, electrostatic in nature and formed between elements that have large differences in electronegativity

Front 401

ionic charge

Back 401

the number of electrons lost of gained when an atom becomes ionized

Front 402

ionic crystal

Back 402

a crystal in which the predominant bonding is ionic

Front 403

ionic radius

Back 403

radius of a spherical volume effectively occupied by an ion in a particular environment

Front 404

iridescence

Back 404

the display of rainbowlike colors in the interior or on the surface of a mineral

Front 405

iron formation

Back 405

general name given to chemical sedimentary rocks dominated by iron oxides, hydroxides, carbonates, sulfides, or silicates

Front 406

irregular (fracture)

Back 406

a fracture that produces rough and irregular surfaces (see also uneven fracture)

Front 407

isochrome

Back 407

color bands that wrap around the trace of the optic axis (uniaxial mineral) or the optic axes (biaxial mineral) in an interference figure

Front 408

isodesmic

Back 408

describing a crystal in which all bonds are ionic and of equal strength

Front 409

isogonal

Back 409

a term describing space groups that contain the same rotation axes; also used to descrbie space groups that have the same symmetry when translation is ignored

Front 410

isograd

Back 410

any line based on mienral or mineral-assemblage occurences that can be mapped in a metamorphic terrane

Front 411

isogyre

Back 411

a band of extinction in a interference figure that appears where light vibration directions are parallel and perpendiculoar to the lower and upper polarizers

Front 412

isolated tetrahedral silicates

Back 412

silicate mienrals characterized by individual SiO4 tetrahedra linked by bonding to common cations.

Front 413

isomorphous series

Back 413

a solid solution series in whcih the crystal structure is the same throughout the series

Front 414

isostructural

Back 414

a term describing two minerals that have differnt, but identically arranged, atoms in their crystal structures

Front 415

isotope

Back 415

one of two or more species of the same chemical element; different isotopes of an element have the same number of protons but vary in their number of neutrons

Front 416

isotropic

Back 416

having the same properites in all directions

Front 417

join (phase diagram)

Back 417

a line that connects two end member compositions on a ternary phase diagram

Front 418

Jolly balance

Back 418

a type of balance scale used to determine specific gravity

Front 419

Kimberlite

Back 419

an alkalic peridotite associated with diatremes, typically containing phenocrysts of olinvie and phlogopite or their alteration products

Front 420

Komatiite

Back 420

a general name given to a lava of ultramafic composition

Front 421

Labradorescence

Back 421

a flashing and laminated iridescence, generally of a single bright hue, similar to that displayed by labradotie, a plagioclase feldspar

Front 422

lamellar

Back 422

having a tablike appearance; being thin in one dimension compared to the other two (see also platy and tabular)

Front 423

lanthanide

Back 423

elements (such as Ce, Pr, and Nd0 with atomic numbers 58 through 71 and valence electrons in 4f orbitals (see also rare earth elements)

Front 424

laterite

Back 424

a highly weathered and leached soil or subsoil rich in aluminum, iron, or other insoluble elements; often rich in quartz and clay minerals

Front 425

latite

Back 425

an extrusive igneous rock of intermediate composition containing approximately equal amounts of plagioclase and K-feldspar; minor quartz, clinopyroxene, biotite, and hornblende may be present

Front 426

lattice

Back 426

a three-dimensional representation of the translational symmetry of a crystal structureq

Front 427

lattice point

Back 427

translationally equivalent points in space; in a crystal lattice, points are surrounded by identical and indistinguishable atomic arrangements

Front 428

Laue equations

Back 428

equations derived by von Laue that describe the angular relationship between an incident beam and a diffracted beam in three-dimensional space

Front 429

Laue method

Back 429

x-raying a single crystal by placing it in the pat of a polychromatic x-ray beam and positioning a flat piece of film behind it

Front 430

lava

Back 430

molten extrusive magma

Front 431

lava flow

Back 431

a horizontal outpouring of lava from a vent or fissue

Front 432

law of definite proportions

Back 432

a general law that says compounds are made of elements combined in specific proportions

Front 433

Law of Bravais

Back 433

an observational law that states faces on crystals tend to be parallel to planes having a high lattice point density

Front 434

Law of Rational Indices

Back 434

a law that states that crystal faces make simple rational intercepts with crystallographic axes; a corollary is that crystal faces have rational and generally small Miller indices (see also Hauy's Law)

Front 435

laws (scientific)

Back 435

a formal statement of general scientific observations that have never been found to be violated

Front 436

layer silicates

Back 436

silicate minerals characterized by SiO4 tetrahedra joining to form sheets; includes micas and clays (see also sheet silcates and phyllosilicates)

Front 437

leach

Back 437

to dissolve and remove soluble components from a rock or soil

Front 438

left handed

Back 438

a relative phrase, referring to objects that rotate or point to the left

Front 439

length fast

Back 439

a term describing a birefringent mineral in which the fast ray vibrates more or less parallel to the length of an elongate crystal

Front 440

length slow

Back 440

a term describing a birefringent mineral in which the slow ray vibrates more or less parallel to the length of an elongate crystal

Front 441

lime kiln

Back 441

long horizontal cylindraical furnace used to heat limestone in order to make lime (CaO)

Front 442

limestone

Back 442

a chemical sedimentary rock composed primarily of calcite; in a more general sense the term is sometimes used to refer to any chemical sedimentary rock composed mostly of carbonates

Front 443

line defect

Back 443

a kind of defect that occurs along a line in a crystal structure

Front 444

lineage structure

Back 444

a plane within a crystal separating slightly misoriented portions of a crystal structure

Front 445

linear(coordination)

Back 445

coordination of a small ion or atom to only two others

Front 446

lineation

Back 446

any linear feature that may be obseved in a rock

Front 447

liquidus

Back 447

the line on a temperature-composition diagram that shows the temperatures above which a system is completely liquid

Front 448

lithic fragment

Back 448

clastic fragment of preexisting rock

Front 449

lithification

Back 449

process of a sediment being convertend to a rock; it often involves compaction, descciation, cementation, and recrystallization

Front 450

lithophile

Back 450

an element that tends to concentratein silicates rather than in metals or sulfides

Front 451

lode deposit

Back 451

an ore deposit comprising many small veins

Front 452

lower polarizer

Back 452

a fixed polarizing lens located in the substage of a polarizing light microscope

Front 453

luminescence

Back 453

the emission of energy of a different wavelength froma mineral or other substance that has been stimulated by an external energy source of some wavelength(s)

Front 454

luster

Back 454

the reflection of light from the surface of something, described by its quality and intensity

Front 455

macroscopic property

Back 455

a mineral property seen or measure in a hand specimen

Front 456

magma

Back 456

naturally occuring molten rock materal

Front 457

major element

Back 457

an element that is a key and essential part of a mineral (see also minor element or trace element)

Front 458

malleable

Back 458

a term used to describe the tenacity of mienrals that are capable of being hammered into shapes

Front 459

mammilary

Back 459

having a breastlike appearance

Front 460

Mannebach twin

Back 460

an uncommon tiwn law in feldspar

Front 461

marble

Back 461

aa metamorphic rock containing primarily clacite or dolomite

Front 462

marl

Back 462

a calcareous rock containig significat amounts of clay and other detrital material

Front 463

mass number

Back 463

symbolized by (A), the totaly number of protons and neutrons in an atom

Front 464

massive

Back 464

a term describing a mineral or mineral aggregate lacking in internal structure or other distinguishable physical characteristics

Front 465

matrix

Back 465

small or fine-grained material that encloses larger grains or crystals

Front 466

mechanical weathering

Back 466

type of weathering involving the physical decomposition or breakdwon of minerals and rock to produce smaller pieces

Front 467

melatope

Back 467

the trace of the optic axis (uniaxial mineral) or the optic axes (biaxial mineral) in an interference figure; thepoint where the isogyres cross in a uniaxial interference figure; the points on the isogyres closest to the center of a Bxa or Bxo interference figure

Front 468

Mesodesmic

Back 468

describing a crystal in which the strength of all bonds from a cation to its coordinating anions is equal to exactly one-half the charge of the anions

Front 469

metabasite

Back 469

a metamorphosed mafic rock

Front 470

metal (element)

Back 470

a general term often applied to any element that ionizes easily to become a cation; alternatively used to mean any of a class of elements that, when in pure form, usually have the shiny surface, and are good conductors of heat an electricity

Front 471

metal (native element)

Back 471

native elements of metallic character; pricipally gold, silver, copper and platinum

Front 472

metallic bond

Back 472

an ideal chemical bond in which electrons are highly delocalized and free to move from one atom to another

Front 473

metallic luster

Back 473

a mineral luster caracterized by brightness and shininess and the ability to reflect light

Front 474

metamorphic

Back 474

an adjective pertaining to the process of metmorphism

Front 475

metamorphic facies

Back 475

a range of pressure-temperature conditions characterizsed by one or more specific mineral assemblages

Front 476

metamorphic grade

Back 476

the degree of metamorphism; generally equivalent to the temperature of metamorphism

Front 477

metamorphism

Back 477

mineralogical or textural changes in rocks in response to changes in physical or chemical conditions

Front 478

metapelite

Back 478

a metamorpic rock equivalent in composition to a clay-rich sediment

Front 479

metapsammite

Back 479

a metamorpich rock equivalent in composition to a clay-rich sediment

Front 480

metasomatism

Back 480

a change in rock composition due to the movement of pore fluids associated with metamorphism

Front 481

metastable

Back 481

(thermodynamics) adjective describing a mmineral or mineral assemblage that is not undergoing change ut does not have the minumum possible Gibbs free energy

Front 482

metastable equilibrium

Back 482

equilibrium not representative of the minimal possible Gibbs energy of a system; a chemical system at metastable equilibrium is not reacting but may eventually do so to attain stable equilibrium

Front 483

micaceous

Back 483

having the properties of a mica, the ability to be split into thin sheets

Front 484

micrite

Back 484

fine-grianed microcrystalline calcite; the term is sometimes used to refer to a chemical sedimentary rock composed of microcrystalline calcite

Front 485

microcrystalline

Back 485

having crystals that can only be seen with the aid of a microscope

Front 486

microscopie property

Back 486

a mienral property not generally seen or measured without a microscope

Front 487

migmatite

Back 487

a mixed rock composed of differend color hands, often associated with partial melting under high-grade metamorphic conditions

Front 488

Miller index (indices)

Back 488

numbers used to describe the orientation of a plane with respect to crystal axes; Miller indices are generally enclosed in parentheses

Front 489

mineral

Back 489

naturally occuring and crystalline substances of fixed or limited composition

Front 490

mineral class

Back 490

a broad category of minerals generally based on commonality of anions or anionic compleses; for exmaple., carbonates and sulfates are mineral classes

Front 491

mineral formula

Back 491

an expression that uses chemical symbols, parentheses, and subsrcipts to show the composition of a mineral

Front 492

mineral group

Back 492

a group of minerals within a class that are distinguished by common properties

Front 493

mineralogy

Back 493

the study of minerals, their formation, occurrence, properites, composition and classification

Front 494

minor element

Back 494

an element that substitutes for a major element in a mineral, generaly present at the 1-5% level (see also major element or trace element)

Front 495

mirror plane

Back 495

a basic symmetry operator across which a mirror image is created

Front 496

miscbility gap

Back 496

a compositional range in a solution series that is not stable as a single phase; a compositional range where unmixing occurs

Front 497

miscibility

Back 497

the ability of two or more phases to mix to produce one solid phase

Front 498

Mississippie Valley-type deposit

Back 498

an epigenetic ore deposit hosted by carbonate rocksl typically, a source of lead and zinc

Front 499

mode (igneous rock)

Back 499

the mineral composition of a rock; generally expresed in volume %

Front 500

Moh's hardness scale

Back 500

a relative scale of 1-10, based on reference minerals, that can be ued to describe a mineral's hardness

Front 501

mole

Back 501

the quantity in grams of an element or compound that equals the molecular weight of the substance; one mole of a substance contains Avogadro's number(6.022/10^23) of atoms/molecules of that substance

Front 502

monochromatic

Back 502

a term describing radiation consisting of one wavelength

Front 503

monoclinic

Back 503

of or related to the monoclinic crystal system

Front 504

monoclinic (system)

Back 504

a crystal system characterized by lattic symmetry 2/m and containing point groups with symmetry no great than 2/m; four cell parameters (a, b, c, ? ) are needed to describe the shape and size of monoclinic unit cell

Front 505

monomineralic

Back 505

containing only one mineral

Front 506

monovalent

Back 506

an ion having a charge of +/- 1

Front 507

Monzonite

Back 507

an intrusive igneous rock of intermediate compostion containing approximately equal amoutns of plagioclase and K-feldspar, minor quartz, clinopyroxene, biotite, and hornblende may be present

Front 508

mother lode

Back 508

an ore body that is the source for ore mienrals found in a placer

Front 509

motif

Back 509

a pattern that is repeated by symmetry

Front 510

mud

Back 510

unconsolidated sediment composed of clay and silt

Front 511

mudstone

Back 511

general term for a fine-grained clastic sedimentary rock composed of clay or silt; sometimes used only for such rocks if they are not foliated

Front 512

native element

Back 512

an element that occurs naturally as a mineral

Front 513

natural

Back 513

a product of nature, not of humans or human activities

Front 514

nesosilicates

Back 514

silicate minerals characterized by individual SiO4 tetrahedra linked by bonding to common cations (see also island silicates and isolated tetrahedral silicates)

Front 515

network silicates

Back 515

silicate minerals characterized by SiO4 tetrahedra joining to form three-dimensional networks ( see also tectosilicates and framework silicates)

Front 516

neutron

Back 516

a subatomic particle of neutral charge, generally found in atomic nuclei, that has about the same mass as a proton

Front 517

noble gas

Back 517

any of the generally unreactive elements (such as Ne, Ar, or Kr) in the 18th group of the Periodic Table of the Elements (see also inert gas)

Front 518

noncrystalline

Back 518

having a random atomic structure (see also amorphous)

Front 519

nonmetal (native element)

Back 519

native element minerals composed of nonmetallic elemets; principally sulfur, graphite, and diamond

Front 520

nonmetallic (element)

Back 520

elements that do not possess the propoerties of a metal. Nonmetallic elements generally ionize easily to become anions, have a nonmetallic luster, and are poor conductors of heat and electricity when pure

Front 521

nonmetallic (luster)

Back 521

a mineral luster that is not metallic (see also admantine, vitreous , resinous, silky, pearly, and greasy)

Front 522

nonopaque (mineral)

Back 522

a mineral that transmits light in thin section

Front 523

nonprimitive

Back 523

used to describe a unit cell containing more than one lattice point

Front 524

nonspecial angle

Back 524

an angle unrelated to angles btween symmetry elements (see also general angle)

Front 525

nonprimitive

Back 525

used to describe a unit cell containing more than one lattice point

Front 526

nonspecial angle

Back 526

an angle unrelated to angles between symmetry elements (see also general angle)

Front 527

normalization

Back 527

the process of converting a mineral analysis to a chemical formula

Front 528

nuclei

Back 528

plural of nucleus; the central parts of atoms consisting of protons, or of combinations of protons, neutrons, and other particles

Front 529

numerical aperture

Back 529

a number describing the size of the cone of light that can enter a lens

Front 530

O ray

Back 530

see ordinary ray

Front 531

obsidian

Back 531

volcanic glass produced by the rapid cooling of a magma

Front 532

obtuse bisectrix

Back 532

the direction bisecting the obtuse angle between the optic axes of a biaxial crystal; perpendicular to the acute bisectrix

Front 533

obtuse bisectix figure (Bxo)

Back 533

the biaxial interference figure seen when looking down the obtuse bisectrix

Front 534

octahedral (cleavage)

Back 534

a term used to describe four cleavages that produce octahedral cleavage fragments; for example, fluorite has octahedral cleavage

Front 535

octahedral (coordination)

Back 535

the bonding of an ion to six others arranged so that connecting their center forms an octahedron

Front 536

ooctahedron

Back 536

a cubic from [111] of eight faces, each an equilateral triangle; a from of crystal class 4/m32/m

Front 537

ocular

Back 537

a lens in an eyepiece of a microscope

Front 538

oppalescence

Back 538

the play of colors seen in some minerals that resembles that of opal

Front 539

opaque

Back 539

the inability to transmit light or to be seen through

Front 540

open form

Back 540

a form that, by itself, cannot enclose three-dimensional space

Front 541

operation (symmetry)

Back 541

an operation that repeats a motif, crystal face, or other entity in a symmetrical pattern

Front 542

operatory (symmetry)

Back 542

any symmetry element element that repeats a motif crystal face or other entity in a symmetrical pattern; rotation axis, mirror plane, inversion center, rotoinversion axis, translation, glide plane, or screw axis

Front 543

optic axis

Back 543

a direction through a crystal along which no double refraction occurs

Front 544

optic axis figure

Back 544

the interference figure seen when looking down an optic axis

Front 545

optic normal

Back 545

the direction perpendicular to the optic plane of a biaxial mineral, corresponding to the y-axis

Front 546

optic normal interference figure

Back 546

the interference figure obtained when looking down a optic normal

Front 547

optic plane

Back 547

the plane containing the optic axes of a biaxial crystal

Front 548

optic sign

Back 548

either + or - , describing the relationship between indices of refraction. In uniaxial positive (+) crystals; in uniaxial negative (-) crystal; in biaxial positive (+) crystals, ? is closer in value to ? than to ?; in biaxial negative (-) crystals, ? is closer in value to ? than to ?

Front 549

order of diffraction

Back 549

the value of n in Bragg's law; the number of cycles a diffracted beam lags behind an adjacent beam with which it is in phase

Front 550

ordinary ray

Back 550

in a uniaxial crystal, the ray of light that vibrates perpendicular to the optic axis and obeys Snell law

Front 551

ore

Back 551

anything that can be taken from the ground and sold for a profit

Front 552

ore deposit

Back 552

an economical concentration of ore mienrals

Front 553

ore grade

Back 553

the concentration of ore minerals or elements in ore rock

Front 554

ore mineral

Back 554

a mienral, usually metallic, that is economically desirable

Front 555

organic

Back 555

a compound contianing carbon bonded to hydrogen as an essential and major component

Front 556

orthogonal

Back 556

perpendicular

Front 557

orthonet

Back 557

a two-dimensional lattice characterized by two translations of different magnitudes at 90 degrees to each other

Front 558

orthopyroxene

Back 558

orthorhombic pyroxene subgroup dominated by end members enstatite and ferrosilite

Front 559

orthorhombic

Back 559

of or related to the orthorhombic crystal system

Front 560

orthorhombic (system)

Back 560

a crystal system characterized by lattice symmetry 2/m2/m2/m, and containing point group with symmetry no greater than 2/m2/m2/m, and three cell parameters (a,b,c) are needed to describe the shape and size of an orthorhombic unit cell

Front 561

orthoscopic (illumination)

Back 561

illumination caused by light rays all traveling parallel to the tube of polarizing light microscope

Front 562

orthosilicates

Back 562

obsolete (see also isolated tetrahedral silicates)

Front 563

out-of-phase

Back 563

the condition in which the peaks, and valleys, of two waves do not match in time and space

Front 564

oxidation

Back 564

the process of an atom losing one or more electrons through chemical reaction

Front 565

oxide

Back 565

compound of oxygen with another element or radical

Front 566

oxidize

Back 566

describes an element that has lost one or more electrons

Front 567

paired tetrahedral silicates

Back 567

silicate minerals characterized by SiO4 tetrahedra joined to form pairs (see also sorosilicates)

Front 568

parallel extinction

Back 568

extinction condition in which the principal cleavage or length of a crystal is parallel to the crosshair of a polarizing light microscope

Front 569

paramagnetism

Back 569

having a small magnetic susceptibility and being weakly attracted by a magnet

Front 570

parent isotope

Back 570

the initial radioactive member of a radioactive decay series

Front 571

partial crystallization

Back 571

separation of a crystallizing magma into parts by the successive crystallization of different minerals (see also fractional crystallization)

Front 572

partial melting

Back 572

melting of only some of the mienrals in a highgrade metamorphic

Front 573

parting

Back 573

breaking of a mineral along a plane of weakness; generally cause by twinning or deformation

Front 574

Pauling's rules

Back 574

five empirical rules, first tabulated by Linus Pauling, describing common structural and bonding features of ionic structures

Front 575

pearly

Back 575

a type of luster that appears iridescent, similar to pearls or some seashells

Front 576

pedion

Back 576

an open form consisting of one crystal face unrelated to any other by symmetry

Front 577

pegmatite

Back 577

an exceptionally coarse grained igneous rock; generally formed by crystallization of water-rich magmas

Front 578

pelite

Back 578

a rock with composition equivalent to a clay-rich sediment

Front 579

penetration twin

Back 579

a twin in which two individual crystals, sharing a common volume of atoms, appear to penetrate or grow through each other

Front 580

pericline twin

Back 580

a common twin law in triclinic feldspars; K-feldsapr that have both albite and pericline twins develop the (microscopic) scotch-plaid twinning characteristic of microcline

Front 581

peridotite

Back 581

a general term for an intrusive igneous rock of highly mafic composition; typically composed of olivine (+/-) other mafic minerals and minor plagioclase

Front 582

period (of elements)

Back 582

elements that occupy the same row in the Periodic Table of the Elements

Front 583

periodic chart

Back 583

also called the periodic table; a table in which the chemical elements are arranged in order of their atomic numbers and grouped in columns based on atomic structure

Front 584

petrogenesis

Back 584

the branch of petrology dealing with the origin and formation of rock

Front 585

petrographic microscope

Back 585

a microscope that uses polarizing light for observation and analysis of minerals in grain mounts or in thin sections (see also polarizing light microscope)

Front 586

petrography

Back 586

the branch of petrology dealing with the description and classification of rocks

Front 587

phaneritic

Back 587

having mineral grains visible without a microscope

Front 588

phase diagram

Back 588

any of a number of different types of diagrams used to depict mineral compositions or stability of various phases in a system; the axes are usually temperature, pressure, or composition

Front 589

phase rule

Back 589

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 Gibbs phase rule)

Front 590

phenocryst

Back 590

the relatively large, conspicuous crystals in a porphyritic rock

Front 591

phosphate (mineral)

Back 591

group of minerals characterized by (PO4)3-, in their formulas

Front 592

phosphate (radical)

Back 592

the (PO4)3-, anionic group

Front 593

phosphorescence

Back 593

a type of luminescence in response to exposure to ultraviolet light, x-ray, or cathode ray that continues after the exposure ceases

Front 594

phosphorite

Back 594

a chemical sedimentary rock composed primarily of phosphate mienrals, typically varieties of apatite

Front 595

phyllite

Back 595

a foliated metamorphic rock, lacking in schistosity, having a sparkly or silky sheen due to the presence of fine-grained micas

Front 596

phyllosilicates

Back 596

silicate minerals containing SiO4 tetrahedra joined to form sheets; includes micas and clays (see also layer silicates and sheet silicates)

Front 597

piezoelectric

Back 597

having the ability to develop a small amount of electrical potential when strained

Front 598

pinacoid

Back 598

an open crystal form compised of two parallel faces

Front 599

pipe

Back 599

an igneous body with a more or less round cross section formed as a magma ascends rapidly to the Earth's surface

Front 600

pisolitic

Back 600

a term describing crystals that are very small spheres

Front 601

pisolitic

Back 601

a term describing crystals that are very small spheres

Front 602

placer

Back 602

a sedimentary mineral deposit, often fluvial, formed by the concentraion of heavy minerals due to gravitational forces

Front 603

Planck's law

Back 603

an equation that relates the energy (E) of an electromagnetic wave to its frequency (v):E=hv, where h is Planck's constant

Front 604

plane defect

Back 604

a kind of defect that occurs along the boundary plane of two regions of a crystal or between two grains

Front 605

plane polarized

Back 605

a term describing a moving wave, perhaps light, that is constrained to vibrate in one plane

Front 606

plaster of Paris

Back 606

a white calcium sulfate-based plaster that is more hydrated than anhydrate but less hydrated than gypsum

Front 607

platy (cleavage)

Back 607

a cleavege that allows a crystal to be broken into plates

Front 608

platy (crystal)

Back 608

appearing to be platelike, thin in one dimension compared with the other two (see also tabular and lamellar)

Front 609

play of colors

Back 609

the separation of white light into visible individual colors when it interacts with a mineral; often leading to changes in color as a mineral is turn (see also schiller)

Front 610

pleochroism

Back 610

the property of an anisotropic crystal to absorb different wavelengths, and thus to have different color, depending on orientation; most easily seen by rotating the stage of a polarizing light microscope while viewing an anisotropic crystal in thin section under plane polarized light

Front 611

plumose

Back 611

a term describing an aggregate of crystals having a feathery appearance

Front 612

plutonic rock

Back 612

an igneous rock that crystallizes at depth in the earth (see also intrusive rock)

Front 613

point defect

Back 613

a defect that occurs at one point in a crystal structure

Front 614

point group

Back 614

one of the 32 possible symmetry groups to which a crystal can belong; translation-free equivalent of space groups (see also crystal classes)

Front 615

polarized (ions)

Back 615

a term describing an ion with uneven electon distributation so that it does not behave as an ionic sphere in a crystal structure

Front 616

polarized (wave)

Back 616

a term describing a moving wave, perhaps light, that is not free to vibrate in all directions

Front 617

polarizing light microscope

Back 617

a microscope that uses polarizing light for observation and anlysis of minerals in grainmounts or in thin section (see also petrographic microscope)

Front 618

pole

Back 618

a perpendicular to a face on a crystal

Front 619

polychromatic

Back 619

radiation containing multiple wavelengths (see also monochromatic)

Front 620

polyhedron

Back 620

a three-dimensional geometric figure having four or more faces

Front 621

polychromatic

Back 621

radiation containing multiple wavelengths (see also monchromatic)

Front 622

polyhedron

Back 622

a three-dimensional geometric figure having four or more faces

Front 623

polymer

Back 623

a chemical unit formed by the tight linking of individual molecules

Front 624

polymerization

Back 624

the connecting of polyhedra or other structural units chains, sheets, or networks by sharing or atoms

Front 625

polymorphs

Back 625

minerals that have identical compositions but different crystal structures; for example, calcite and aragonite are polymorphs

Front 626

polysynthetic twin

Back 626

repeated twinning of three or more individuals according to the same twin law and in a parallel manner, porducing a twinned grain composed of many thin parallel sheetlike twin domains

Front 627

porcelain

Back 627

a special type of high-quality white ceramic

Front 628

polymorphs

Back 628

minerals that have identical compositions but different crystal structures; for example, calcite and aragonite are polymorphs

Front 629

polysynethetic twin

Back 629

repeated twining of three of more individuals according to the same twin law and in a parallel manner, producing a twinned grain composed of many thin parallel sheetlike twin domains

Front 630

porphyroblast

Back 630

a large mineral crystal, produced by metamorphism, in a finer-grained matrix

Front 631

porphyry (igneous rock)

Back 631

a rock containing relatviely large crystals (phenocrysts) in a fine-grained ground mass that may be crystalline or glassy

Front 632

porphyry (ore deposit)

Back 632

an ore deposit in which the ore is concentrayed in closely spaced small veins and neilets

Front 633

Portland cement

Back 633

the most common kind of cement; composed of a mixture of lime, silica, alumina, and iron oxides

Front 634

powder diffraction

Back 634

diffraction of X rays by a powdered sample

Front 635

powder diffraction file (PDF)

Back 635

the x-ray powder diffraction reference file used by m ost mineralogists

Front 636

Precambrian shield

Back 636

an ancient geological terrane that has been stable for a long time; typically in the central area (craton) of major continents

Front 637

precious metals

Back 637

gold, silver, platinum, and sometimes other platinum group elements

Front 638

precipitate

Back 638

to form solid material from material dissolved in a liquid; precipitated material generally but not always settles to the bottom of the liquid

Front 639

primary mienral

Back 639

a mineral formed at the same time as its host rock (see also secondary mineral)

Front 640

primitive

Back 640

describing a unit cell containing in total one lattice point; typically unit cells are chosen so that a primitive unit cell contains one-eighth of a lattice point at each corner

Front 641

principal axis

Back 641

the most prominent or unique crystal axis in crystal or the most prominent or unique rotational axis of symmetry in a crystal; generally they coincide

Front 642

principle of parsimony (Pauling's rule 5)

Back 642

the number of different components in a crystal tends to be small

Front 643

prism

Back 643

a crystal form characterized by two or more crystal faces parallel to a common direction

Front 644

prismatic (cleavage)

Back 644

a term used to describe multiple cleavages all parallel to a common direction in acrystal

Front 645

prismatic (crystal)

Back 645

having the appearance of a prism or prisms; appearing as a long crystal with parallel sides

Front 646

prograde reactions

Back 646

reactions that take place in response to an increase in temperature

Front 647

prism

Back 647

a crystal form characterised by two or more crystal faces parallel to a common direction

Front 648

prismatic (cleavage)

Back 648

a term used used to describe multiple cleavages all parallel to a common direction in a crystal

Front 649

prismatic (crystal)

Back 649

having the appearance of a prism or prisms; appearing as a long crystal with parallel sides

Front 650

prograde metamorphism

Back 650

metamorphism in response to increasing temperature

Front 651

progressive metamorphism

Back 651

metamorphism that proceeds by steps from low grade to high grade

Front 652

proper rotation axis

Back 652

a rotation axis of symmetry that does not involve inversion

Front 653

proton

Back 653

a subatomic particle, generally found in the nuclei of atoms, having the smallest amount of possitive electric charge occurring in nature

Front 654

psammite

Back 654

a rock equivalent in composition to a sandstone or feldspathic sandstone with minor amounts of clay

Front 655

psuedohexagonal

Back 655

symmetry that appears to be present but, with better measurement or observation, would be found to be lacking

Front 656

pseudosymmetry

Back 656

symmetry that appears to be present but, with better measurement or observation, would be found to be lacking

Front 657

pycnometer

Back 657

a small bottle with a tight-fitting stopper that is used to determine specific gravity

Front 658

pyramid

Back 658

an open crystal form of 3, 4, 6, 8, or 12 nonparallel faces that meet at a point

Front 659

pyramidal cleavage

Back 659

cleavage that gives cleaved crystals a pyramid shape

Front 660

pyritohedron

Back 660

a cubic crystal form, consisting of 12 irregular pentagonal facesl a form of crystal class 23 or 2/m3

Front 661

pyroelectric

Back 661

having the ability to develop a small amount of electrical potential when heated

Front 662

pyroxenite

Back 662

an ultramafic intrusive rock composed primarily of pyroxene with lesser amounts of olivine, biottite, or hornblende

Front 663

quartz plate

Back 663

an accessory plate for polarizing light microscopes that is composed of quartz of known optical orientation

Front 664

quartz wedge

Back 664

an elongate wedge of clear quartz of known optical orientation that may be inserted in a polarizing light microscope tube to analyze a crystal's optical properties

Front 665

quartzite

Back 665

a hard but unmetamorphosed sandstone or the metamorphic equivalent

Front 666

quartzose

Back 666

containing quartz as a primary component

Front 667

radiating

Back 667

emananting from a common point (see also divergent)

Front 668

radical

Back 668

a chemical group that has acquired an elctrical charge; orten surrounded by parentheses in mineral formulas

Front 669

radioactivity

Back 669

the spontaneous decay of atoms of certain isotopes into new isotopes, accompanied by the emission of high energy particles

Front 670

radioisotope

Back 670

an isotope that is the product of radioactive decay

Front 671

radius ratio principle (Pauling's rule 1)

Back 671

cation-anion distances are equal to the sum of their effective ionic radii, and cation coordination numbers are determined by the ratio of cation and anion radii

Front 672

rare earth elements

Back 672

elements (such as Ce, Pr, and Nd) with atomic numbers 58 through 71 and valence electrons in 4f orbitals (see also lanthanide elements)

Front 673

recrystallization

Back 673

formation of new crystals from preexisting material; the new crystals need not be the same species or composition as the material form which they from

Front 674

recrystallize

Back 674

to form new crystalline mineral grains in a rock, generally by metamorphism

Front 675

reduce

Back 675

said of an element; to gain one or more electrons

Front 676

reduction

Back 676

the process of an atom gaining one or more electrons through chemical reaction

Front 677

reentrant angle

Back 677

an angle between two crystal faces that points or is directed inward toward the center of the crystal; usually associated with twins

Front 678

reflected light microscopy

Back 678

microscopic examination using a light source that reflects form the surface of a sample; reflected light microscopy is useful for identifying opaque minerals in thin section

Front 679

reflection (light)

Back 679

coherent scattering of energy by atoms in a two-dimensional surgace

Front 680

reflection (symmetry)

Back 680

a term describing the operation that relates two crystal faces or other entities across a mirror plane

Front 681

refraction

Back 681

the deflection of a ray, perhaps light, due to its passage from one medium to another of fdifferent ray velocity

Front 682

refractive index

Back 682

the ratio off the velocity of light in a vacuum to the velocity of light in a given medium (see also index of refraction)

Front 683

refractive index oil

Back 683

a liquid of known index of refraction

Front 684

refractometer

Back 684

a device for determining the index of refraction of a crystal or other material

Front 685

regional metamorphism

Back 685

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

Front 686

regular polyhedron

Back 686

a coordinating polyhedron in which all cation-anion bond lengths are equal

Front 687

relief

Back 687

the apparent topography of a crystal or crystals seen under a microscope

Front 688

reniform

Back 688

having a kidney-shaped appearance

Front 689

reserves

Back 689

ore that has been identified and that could be extracted at a profit

Front 690

residual (phase)

Back 690

the remaining liquid, or phases that crystallize from such a liquid, after a magma has mostly solidified

Front 691

residual (mineral)

Back 691

a mineral that has been concentrated in place by weathering and leaching of rock

Front 692

reserves

Back 692

ore that has been identified and that could be extracted at a profit

Front 693

residuum

Back 693

insoluble material remaining after intense weather

Front 694

resinous

Back 694

a term used to describe mineral lusters that have the appearance of resin

Front 695

reinstate

Back 695

insoluble material produced by chemical weathering; the term is also used in a general sense to refer to any sedimentary material of low solubility

Front 696

retardation

Back 696

the distance that one wave lags behind another; specifically the distnace that the fast ray lags behind the slow ray upon emergence form a crystal

Front 697

reticulated

Back 697

crystals that have a latticelike appearance

Front 698

retrograde metamorphism

Back 698

metamorphismn that takes place in response to decreasing temperature

Front 699

retrograde reactions

Back 699

metamorphic reactions that take place in response to decreasing temperature

Front 700

rhomb

Back 700

a parallelogram having equal length sides and interior angles at 60 to 120

Front 701

rhombohedral (point groups)

Back 701

any of the point groups that include the rhombohedral from (3, 32, 32m)

Front 702

rhombohedral plane lattice

Back 702

a two-dimensional lattice characterized by two translations of equal magnitude at 60 degrees to each other (see also hexanet)

Front 703

rhombohedron

Back 703

a closed form that creates a parallelepiped with six identical rhomb-shaped races

Front 704

rhyolite

Back 704

an extrusive igneous rock of silicic composition containing 10%-50% quartz and K-feldspar as the major feldspar: plagioclase, biotite, and hornblende may be present (see also granite)

Front 705

Rietveld method

Back 705

a method of making crystal structure analyses based on powder diffraction data

Front 706

tetragonal packing

Back 706

the planar arrangement of spheres of identical size in a square pattern; each sphere is surrounded by eight others

Front 707

tetrahedral (coordination)

Back 707

the bonding of an ion to four others arranged so that connecting their centers forms a tetrahedron

Front 708

tetrahedron

Back 708

a geometric solid bonded by four equilateral traingles; specifically refers to a crystal form of the cubic system having four equilateral triangular faces

Front 709

tetrahedron (silica)

Back 709

a tetrahedral arrangement of Si4+ ad O2- ions having an overall composition and charge of SiO4 (2-),

Front 710

tetravalent

Back 710

an ion having a charge of +/- 4

Front 711

thermodynamics

Back 711

the branch of physics and physical chemisty that deals with the relationships between heat and other forms of energy, and of the conversion of one into the other

Front 712

thermoluminescence

Back 712

a type of luminescence caused by heating a mineral

Front 713

thin section

Back 713

a thin piece of rock glued on a glass slide and uniformly ground to a thickness of about 0.03 mm

Front 714

tie line

Back 714

a line connecting two mineral compoistions on a phase diagram; time lines sohw possible mineral assemblages

Front 715

till

Back 715

unsorted and unstratified glacial deposits

Front 716

tonalite

Back 716

an intrusive igneous rock of silicic composition in which the only major feldspar is plagioclase; bitotite and hornblende are typically present

Front 717

trace element

Back 717

an element that is not essential in a mineral but that is found in very small quantities is in its structure or absorbed on its surface (see also major element and minor element)

Front 718

trachyte

Back 718

an extrusive igneous rock of intermediate composition in which the amount of K-feldspar exceeds the amount of plagioclase; quartz, biotite, and hornblende may be present

Front 719

transition element

Back 719

an element from the fourth and thirteenth group of the PEriodic Table of the Elements and characterized by valence electrons in d-orbitals (see also transition metals)

Front 720

transition metal

Back 720

see transition element

Front 721

translating

Back 721

moving in one direction by a fixed increment

Front 722

translation

Back 722

a shift in position without rotation

Front 723

translucent

Back 723

the ability to transmit light without being transparent

Front 724

transmitteed light microscopy

Back 724

microscopic examiniation using light that passes through a crystal before reaching the eye; the standar kind of microscopy used by petrologists

Front 725

transparent

Back 725

the ability to be seen through; to transmit light with little loss in intensity

Front 726

trapezohedron

Back 726

a crystal form of 6, 8, or 12 faces, each a trapezium

Front 727

travertine

Back 727

a type of limestone formed by rapid precipitation of calcite, often but not necessarily associated with hot springs

Front 728

triangular )coordination)

Back 728

coordination of an ion to only three others

Front 729

triclinic

Back 729

of or related to the triclinic system

Front 730

triclinic (system)

Back 730

a crystal system characterized by lattice symmetry ? and containing point groups with symmetry no greater than?; six cell parameters, are needed to describe the shpae and size of triclinic unit cell

Front 731

trigonal (system)

Back 731

a subsystem of the hexahonal system containing all point groups lacking a 6-fold of ?-fold axis of symmetry

Front 732

trioctahedral

Back 732

describing a layered mineral structure in which three of three available octahgedral sites are occupied

Front 733

trisoctahedron

Back 733

a cubic form of 24 faces, each of which is an isosceles triangle; a form of crystal class 432, 2/m3 or 4/m32/m

Front 734

trivalent

Back 734

an ion having a charge of +/- 3

Front 735

tumble

Back 735

to polish a gem in a revolving box or barrel

Front 736

twin

Back 736

an intergrowth of two or more single crystals of the same mineral that share common atoms, typically along planes

Front 737

twin lamellae

Back 737

thin parallel individual twin domains that are part of a polysynthetic twin

Front 738

twin law

Back 738

a definition of a twin relationship in a mineral or mineral group, specifying the twin axis, center, or plane, defining the composition surface or plane if possible, and giving the type of twin

Front 739

twin plane

Back 739

a plane that separates two twin domains

Front 740

twinning

Back 740

the development of intergrowths of two or more single crystals of the same mineral that share common atoms, typically along planes

Front 741

ultramafic

Back 741

a general adjective referring to igneous rocks rich in magnesium and iron and containing primarily magic minerals

Front 742

ultraviolet light

Back 742

electromagnetic radiation with wavelengths slightly less than visible light

Front 743

uneven fraction

Back 743

a fracture that produces rough and irregular surfaces (see also irregular fracture)

Front 744

uniaxial

Back 744

a term describing a crystal that has only one optic axis; such crystals belong to the tetragonal or hexgonal crystal systems

Front 745

unit cell

Back 745

parallelepiped defined by three noncopolanar unit translations in a lattice; all crystals may be thought of as a collection of unit cells

Front 746

unit cell parameters

Back 746

the dimensions and angles that characterize a unit cell shape; typically symbolized by -------

Front 747

univariant line

Back 747

a line on a phase diagram; generally representing a reaction and having one degree of freedom

Front 748

unmixing

Back 748

the separation of an initially homogeneous solid, liquid, or gas phase into two or more of differnt compositions

Front 749

unpolarized

Back 749

a term describing light or any other wave that is free to vibrate in any direction

Front 750

unstable (thermodynamics)

Back 750

adjcetive describing a chemical system that does not have the minimum possible Gibbs energy; an unstable chemical system will react to obtain metastable or stable equilibrium if slightly perturbed

Front 751

unstable isotope

Back 751

a radioactive isotope of an element (see also radioisotope)

Front 752

upper polarizer

Back 752

a polarizing filter that may be inserted in the tube of a polarizng light microscope in order to view a sample undercrossed polars (see also analyzer

Front 753

vacancy

Back 753

a site in a mineral structure that is vacant but capable of holding an atom or ion under some circumstances

Front 754

valence

Back 754

the charge of an ion

Front 755

valence electron

Back 755

the outermost electrons of an atomt hat contribute most to the atom's bonding

Front 756

Van der Waals bond

Back 756

a weak type of electrostatic bond, generally insignifcant in minerals, created by brief fluctuations in the balance of positive and negative charges. Important in talc and graphite

Front 757

vapor

Back 757

used in a general sense to refer to a liquid, gas, or supercritical fluid; also used to refer to any gaseous phase emanating from a liquid or a solid

Front 758

variety

Back 758

a division of a mineral species based on particular physical characteristics such as color; for example chalcedony is avariety of quartz

Front 759

Verneuil technique

Back 759

a technique for synthesizing gems that involves melting powder and allowing it to accumulate and crystallize on a boule

Front 760

vesicle

Back 760

a cavity in a lava formed by a gas bubble trapped during cooling of the lava

Front 761

viscosity

Back 761

the thickness, or internal resistance to flow, of a liquid

Front 762

vitreous

Back 762

a type of luster resembling that of glass

Front 763

volatile

Back 763

a chemical material such as water or carbon dioxide, in a magma or rock, that may concentrate as a gas or vapor

Front 764

volcanic rock

Back 764

an igneous rock that crystallizes at or very near the Earth's surface (see also extrusive rock)

Front 765

wave front

Back 765

the front, or leading edge, of multiple in-phase waves traveling in the same direction

Front 766

weathering

Back 766

alteration of a rock by surface agnests; for example, water, wind, sun

Front 767

Weisseberg camera

Back 767

an instrument for recording single crystal diffraction patterns on film

Front 768

white light

Back 768

light composed of a spectrum of different wavelengths

Front 769

whiteschist

Back 769

a very high pressure-temperature metamorphic rock containing white micas and talc

Front 770

x-radiation

Back 770

electromagnetic wave with wavelength much shorter than visible light, on the order of 0.1 to 100A

Front 771

x ray

Back 771

electromagnetic wave with wavelength much shorter than visible light, on the order of 0.1 to 100A (see also x-radiation)

Front 772

x-ray defraction

Back 772

the apparent bending or channeling of x rays when they pass through a crystal structure

Front 773

x ray fluoresncence

Back 773

fluorescence of x rays caused by an incident x-ray beam striking a sample

Front 774

xenolith

Back 774

a rock inclusion picked up by a magma and present after the magma has solidified

Front 775

Zeolite (facies)

Back 775

the lowest pressure-temperature metamorphic facies; characterized by zeolites and other very low-grade minerals

Front 776

zone (compositional)

Back 776

an area in a crystal of distinct chemical composition

Front 777

zone (metamorphic)

Back 777

a region in a metamorphic terrane that is characterized by a specific mineral or mineral assemblage

Front 778

zone axis

Back 778

a line parallel to multiple crystal faces in a crystal

Front 779

zoned

Back 779

a term describing a crystal that has compositional zonation

Front 780

zoning

Back 780

variation in the composition of a crystal, typicall from core to margin (see also compositional zoning)