ACICULAR: Term used to describe a needle-shaped mineral habit.
ADAMANTINE: A brilliant mineral luster, characteristic of minerals with a high index of refraction e.g. diamond and cerussite.
AGATE: A translucent cryptocrystalline variety of quartz.
AGGREGATE: A mass of several mineral grains.
AMMONITE: Any ammonoid belonging to the order Ammonitida, characterized by a thick, ornamented shell with sutures having finely divided lobes and saddles. Range: Ordovician to Cretaceous.
ANHEDRAL: Poorly formed crystal. A mineral grain lacking well-developed crystal faces.
ARCUATE: Bent or curved
ASTERISM: The optical phenomenon of a rayed or star-shaed figure of light displayed by some crystals when viewed in reflected light, as in a "star" sapphire. It is caused by minute oriented acicular inclusions.
BASIC ROCK: Igneous rock that contains between 45% and 55% total silica. These have less than 10% quartz and are rich in ferro-magnesian minerals.
BITREOUS:
BLADED: Said of a mineral in the form of aggregates of flattened blades or elongate crystals.
BOTRYOIDAL: Having the form of a bunch of grapes. Said of mineral deposits, e.g. hematite, having a surface of spherical shapes; also said of a crystalline aggregate in which the spherical shapes are composed of radiating crystals.
CARAT: A unit of weight for diamonds, pearls and other gems. The metric carat, equal to 0.2 gram or 200 mg, is standard in the principal countries of the world.
CEPHALOPOD: A marine mollusk of the class Cephalopoda, characterized by a head surrounded by tentacles and, in most fossil forms, by a straight, curved, or coiled calcarous shell divided into chambers by transverse septa. Range: Cambrian to present.
CLEAVAGE: The breaking of a mineral along its crystallographic planes owing to either a paucity of, or systematically weak, atomic bonds.
COLLOFORM: Said of the rounded, finely banded kidneylike mineral texture formed by ultra-fine-grained precipitation.
COLUMNAR: Said of a crystal habit that is made up of subparallel columnar individuals.
COMPACT: Said of mineral aggregate that has a firm, solid or dense texture, with individual grains closely packed.
CONCHOIDAL: Smooth curved surfaces resulting when a mineral breaks in a glass-like manner.
CONCRETION: A hard, compact aggregate of mineral matter, spherical to irregular in shape, formed by precipitiation from water solution around a nucleus, such as a shell or bone, in a sedimentary or pyroclastic rock. Chert, iron oxide, and pyrite are among the common materials that form concretions.
CRYPTOCRYSTALLINE: Said of the texture of a rock consisting of crystals that are too small to be recognized and separately distinguished even under an ordinary microscope.
CRYSTAL: A homogenous, solid body of a chemical element, compound, or isomorphous mixture, having a regularly repeating atomic arrangement that may be outwardly expressed by plane faces.
CRYSTAL AXIS: Oone of the three or four imaginary lines in a crystal that pass through its center; used as a reference in describing crystal structure and symmetry.
CRYSTAL CLASS: One of 32 possible crystallographic combinations of the non-translational elements of symmetry. Crystal classes are divided among the six crystal systems, and deal with outward symmetry. Synonm: Point Group
CRYSTAL FORM: The geometric shape of a crystal; an assemblage of symmetrically equivalent crystal planes making upa form which displays the symmetry of a crystal class.
CRYSTAL SYSTEM: One of 6 groups or classifications of crystals according to the symmetry of their crystal faces, and having characteristic dimensional equivalences in the lattices or axes of reference. The systems are: isometric (cubic), hexagonal, tetragonal, orthorhombic, monoclinc and triclinic. Within the six systems there is a total of 32 crystal classes.
CRYSTALLINE: The formation and growth of a crystalline solid from a liquid or gas.
CUBIC: cube-shaped; a crystal form of the isomeric system, consisting of six symmetrically equivalent, square and mutually perpendicular faces.
DODECAHEDRON: A crystal form with 12 faces that are either ;entagonal or rhombic. Each face is parallel to one crystallographic axis and intersects the other two.
DOUBLY-TERMINATED:
EARTHY LUSTER: Nonreflective, mineral luster.
EQUANT: Said of a crystal having the same or nearly the same diameter in all directions.
EUHEDRAL: A crystal completely bounded by its characteristic faces.
EVAPORITE: Mineral or rock formed by the evaporation of saline water.
EXSOLUTION: The process whereby an initially homogeneous solid solution separates into two or more distinct crystalline phases without a change in the bulk composition.
FIBROUS HABIT: The tendency of certain minerals minerals, e.g. asbestos, to crystallize in needle-like grains or fibers.
FOLIA:
FRACTURE: The breaking of a mineral other than along planes of cleavage. A mineral can be described in part by its characterisitc fracture, e.g. uneven, fibrous, conchoidal, or hackly.
FRIABLE: Said of a rock or mineral that is easily crumbled.
GANGUE: The valueless rock or mineral aggregates in an ore; that part of an ore that is not economically desirable but cannot be avoided in minint. It is separated from the ore minerals during concentration.
GEM: (a) A cut-and polished stone that has intrinsic value and possesses the necessary beauty, durability, rarity, and size for use in jewelry as an ornament or for personal adornment; (b) An especially fine or superlative gemstone specimen generally of superb color, unusual internal quality and fine cut
GEMMY: Having the characteristics (such as hardness, brilliance, diaphaneity and color) desired in a gemstone.
GLOBULAR: spherulitic; a rounded mass of acicular crystals, commonly of feldspar, radiating from a central point.
GRANITE: A plutonic rock in which quartz makes up to 10 to 50% of the felsic component and the alkali feldspar to total feldspar is 65 to 90%.
GRANULAR: Having grains or in grains
GREASY LUSTER: Said of minerals that appear oily to the touch or to the sight.
HABIT: The general shape of a crystal, e.g. cubic, prismatic, fibrous. For a given type of crystal, the habit may vary from locality to locality depending on environment of growth.
HARDNESS: The resistance of a mineral to scratching; it is a property by which minerals may be described. See Moh's Scale.
HEXAGONAL SYSTEM: One of the 6 crystal systems characterized by one unique axis of threefold or sixfold symmetry that is perpendicular and unequal in length to three identical axes that intersect at angles of 120 degrees.
HYDROTHERMAL: Of or pertaining from to hot water, to the action of hot water, or to the products of this action, such as a mineral deposit precipitated from a hot aqueous solution. "Hydrothermal" is generally used for any hot water but has been restricted by some to water of magmatic origin.
HYDROTHERMAL DEPOSIT: A mineral deposit formed by precipitation of ore and ganue minerals in fractures, faults, breccia openings, or other spaces, by replacment or open-space filling, from aqueous fluids ranging in temperature from 50 to 700 degrees but generally below 400 degress Celcius and ranging in pressure from 1 to 3 kilobars. The fluids are of diverse origin.
IGNEOUS: Said of a rock or mineral that solidified from molten or partly molten material, I.e., from magmal; also, applied to processes related to the formation of such rocks. Igneous rocks constitute one of the three main casses into which rocks are divided, the others being metamorphic and sedimentary.
INCLUSIONS: A crystal or fragement of another substance enclosed in mineral or rock.
IRIDESCENE: The exhibition of prismatic colors producing rainbow effects in the interior or on the surface of a mineral, caused by interference of light from thin films or layers of different refractive index.
ISOMETRIC SYSTEM: One of the six crystal systems, characterized by four threefold axes of symmetry as body diagonals in a cubic unit cell of the lattice. It comprises five crystal classes or point groups.
LABRADORESCENCE: Flashes of iridenscence of a single bright hue that change gradually as a mineral or gemstone is moved about in reflected light; caused by internal structures that relect only certain colors. From the light interference effect exhibited by labradorite caused by thin plates of feldspar produced by twinning or exsoluiton and resulting in a series of vivid colors.
LAMELLAR: Disposed in layers like the leaves of a book.
LATHS: Bladed;
LENTICULAR: A term applied to a mineral habit which resembles in shape the cross section of a lens, esp. of a double-convex lens.
LUSTER: The reflection of light from the surface of a mineral, described by its quality and intensity; the appearance of a mineral in relected light. Terms such as metallic or resinous refer to the general appearance; terms such as bright or dull refer to intensity.
MASSIVE: Said of a mineral that is physically isotropic, e.g. lacking a platy, fibrous, or other structure.
MATRIX: The rock or earthy material in which a crystal or crystal aggregate is embedded or enclosed, as opposed to the crystal itself.
METALLIC LUSTER: Said of a type of luster that is characteristic of metals.
METAMORPHIC ROCK: Any rock drived from pre-existing rocks by mineralogical, chemical and or structural changes, essentially in the solid state, in response too changes in temperature, pressure, shearing stress, and chemical environment, generally at depth in the earth's crust.
METEORIC WATER: Water derived from, or in, the atmosphere.
MICACEOUS: Capable of being easily split into thin sheets, like mica minerals.
MILLER INDICES: A set of three or four symbols (letters or integers) used to define the orieintation of a crystal face or internal crystal plane.
MINERAL: A naturally occuring, inorganic crystalline material with a unique chemical structure.
MINERAL GROUP: aggregate of species that have idnetical or closely similar structure and chemistry.
MOHS SCALE: A series of ten minerals used as standard in determing the relative hardness of a mineral.
MONOCLINIC SYSTEM: One of the six crystal systems, characterized by either a single twofold axis of symmetry, a single plane of symmetry, or a combination of the two. Of the three nonequivalent axes, one is perpendicular to the plane formed by the other two.
OCHEROUS:
OCTAHEDRAL CLEAVAGE: Mineral cleavage parallel to the faces of the octahedron, as in fluorite. Four planes of cleavage.
OCTAHEDRON: A crystal form consisting of eight triangular faces, each having equal intercepts on all three crystallographic axes.
OPAQUE: Said of a mineral that is impervious to visible light.
OPAQUE: Said of a material that is impervious to visble light.
ORE: The naturally occurring material from which a mineral or minerals of economic value can be extracted at reasonable profit. Also, the mineral(s) thus extracted. The term is generally but not aways used to refer to metalliferous material, and is often modified by the name of the valuable constituent, e.g., "iron ore".
ORTHORHOMBIC SYSTEM: One of the six crystal systems, characterized by three axes of symmetry that are mutually perpendicular.
PEARLY LUSTER:
PEGMATITE: An exceptionally coarse-grained igneous rock, with interlocking crystals, usually found as irregular dikes, lenses, or veins, esp. at the margins of batholiths. Pegmatite composition is generally that of granite; the composition may be simple or complex and may include rare minerals rich in such elements as lithium, boron, fluorine, niobium, tantalum, uranium and rare earths. Pegmatites represent the last and most hydrous portion of a magma to crystallize and hence contain high concentrations of minerals present only in trace amounts in granitic rocks.
PERTHITE: A variety of alkali feldspar consisting of intergrowths in which the potassium-rich phase (usually microcline) appears to be the host from which the sodium-rich phase (usually albite) exsolved. The exsolved areas typically form strings, lamellae, blebs, films, or irregular veinlets.
PIEZOELECTRIC: In certain crystals, the development of an electrical potential in certain crystallographic directions when mechanical strain is applied, or, the development of a mechanical strain, hence vibration, when an electric potential is applied. Quartz and tourmaline are examples of naturally piezoelectric crystals.
PISOLITIC:
PLATY: Mineral habit with flat, thin crystals.
PLUMOSE:
PRISMATIC: Said of a crystal that shows one dimension markedly longer than the other two.
PSEUDOMORPH: A mineral whose outward crystal form is that of another mineral species; it has developed by alteration, substitution, incrustation, or paramorphism. A pseudomorph is described as being "after" the mineral whose outward form it has.
PYRITOHEDRON: In the isometric system, a crystal form consisting of 12 five-sided faces, each parallel to one axis and cutting the other two at unequal distances.
PYROELECTRIC:
RESINOUS: The luster on the fractured surfaces of certain minerals that resembles the appearance of resin.
RETICULATED: Having a network or netlike structure.
RHOMBIC:
RHOMBOHEDRON: A crystal form in the hexagonal system bounded by six faces of rhombic outline.
SCALENOHEDRON: A closed crystal form whose faces are scalene triangles; the hexagonal scalenohedron has 12 faces, and the tetragonal scalenohedron has eight.
SCEPTOR:
SCHILLER: The play of color in a mineral, due to the arrangement of minute inclusions in the crystal.
SECONDARY MINERAL: A mineral formed later than the rock enclosing it, usually at the expense of an earlier-formed primary mineral, as a result of weathering, metamorphism, or solution.
SEDIMENTARY ROCK: A layered rock resulting from the consolidation of solid fragmented material transported and deposited by wind, water or ice, chemically precipitated from solution, or secreted by organisms.
SKELETAL: A mineral distinguished from others by its unique chemical and physical properties.
SPECIES:
SPECIFIC GRAVITY: The relative density of a mineral with respect to water; a number representing the ratio of the weight of a mineral to the weight of an equal volume of water. The specfic gravity of a mineral is an expression of both chemistry and crystal structure. Minerals composed of heavy elements (e.g., Fe, Cu,Cr)have a higher density compared with minerals composed of lighter elements. The efficiency with which atoms are packed together in a crystal structure also affects the specfic gravity of a mineral. Two or more minerals may havehave the same chemistry but different structures. In general, a mineral that formed under high-pressure environment is denser than a different mineral with the same chemistry that forms in a low-pressure envrionment. The mineral formed in a high pressure environment has more atoms in the same volume. For example, diamond (C) is formed under high pressure and has a density of 3.50 mgm3. Graphite (C) with a density of 2.30 is formed in a low pressure environment . Both have the chemistory of elemental carbon.
SPLENDENT: A mineral luster of the highest intensity.
STREAK: The color of a mineral in its powdered form, usually obtained by rubbing the mineral on an unglazed piece of porcelain and observing the mark it leaves. Streak is an important characterisitic in mineral identification.
STRIA: One of a series of parallel straight lines on the surface of a crystal, as in pyrite, indicative of an oscillation between two crystal forms; also, one of a series of such lines on the cleavage planes of a maineral, as of plagioclase, indicative of polysynthetic twinning.
STRIATIONS:
TABULAR: Said of a crystal form that shows one dimension markedly smaller than the other two.
TENACITY: The property of the particles or molecules of a substance to resist separation; tensile strength.
TETRAGONAL SYSTEM: One of the six crystal systems, characterized by three mutually perpendicular axes, the vertical one of which is a fourfold roation or symmetry axis; it is longer or shorter than the two horizontal axes, which are of equal length.
TRANSCULENT: Said of a mineral that is capable of transmitting light, but is not transparent.
TRANSPARENT: Said of a mineral that is capable of transmitting light, and through which an object may be seen.
TUFTS:
TWINNING: The intergrowth of two or more single crystals of the same mineral in a predictable manner.