Mindat.org Glossary of Mineralogical Terms

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• microlites
  Microlites are minute crystals in an amorphous matrix. In igneous petrology, the term microlitic is used to describe vitric ...
• phenocryst
  A term for large crystals (megacrysts) or mineral grains floating in the matrix or groundmass of an igneous rocks (often ...
• mineral field
  Scot. A tract of country in which workable minerals are found; a mineral leasehold.
• lateritic
  Having the properties of a laterite, i.e. like an iron rich rock formed in soil horizons.
• pedogenic
  Formed within soils by natural processes.
• geode
  Geodes (Greek γεώδης - ge-ōdēs, "earthlike") are commonly independent spherical masses of resistant mineral matter that ...
• separation
  The distance between any two parts of an index plane (e.g., bed or vein) disrupted by a fault. See Also: horizontal ...
• thermoluminescence
  The property of minerals to emit light when heated. It results from the release of energy stored by displaced electrons trapped ...
• symmetry class
  Synonym of Point group
• crystallographic system
  i. Also Crystal System; any of the major units of crystal classification, embracing one or more symmetry classes. See: ...
• granophyric
  Of or pertaining to granophyre. An irregular microscopic intergrowth of quartz and alkali feldspar. Ref: AGI See also ...
• loss on ignition
  As applied to chemical analyses, the loss in weight that results from heating a sample of material to a high temperature, after ...
• craton
  A part of the Earth's crust that has attained stability, and has been little deformed for a prolonged period. The term is now ...
• greenstone belt
  Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks ...
• black tin
  Eng. Dressed tin ore ready to be smelted; from Cornwall. See also: Cassiterite
• girasol effect
  An effect seen in various gem varieties, e.g. fire opal, moonstone, sapphire, chrysoberyl, quartz, which exhibit a billowy, ...
• saline deposit
  See: evaporite
• septarium
  i. A large, roughly spheroidal concretion, generally 8 to 90 cm in diameter, usually of an impure argillaceous carbonate, such as ...
• placanticline
  A broad, wide oval or round uplift of sedimentary rock layers on continental platforms. It is intermediate between an anticline ...
• principal
  Primary, or leading function. A principal axis is the longest one in a crystal. The principal valence is that at which an element ...
• mid-ocean ridge
  A continuous, seismic, median mountain range extending through the North and South Atlantic Oceans, the Indian Ocean, and the ...
• ophiolite suite
  An ophiolite is a sequence or association of rocks representing a section of Earth's oceanic crust and the underlying upper ...
• mid-oceanic ridge
  Synonym of mid-ocean ridge
• ophiolite
  Synonym of ophiolite suite
• ferrimagnetism
  i. Unbalanced orientation of magnetic moments. Intermediate between ferromagnetism and antiferromagnetism. Ref: Van ...
• homeotypic
  Two crystal structures are considered as homeotypic if all essential features of topology are preserved between them, despite ...
• strike-slip fault
  i. A fault on which the movement is parallel to the fault's strike. Synonym of: strike-shift fault Compare with: dip-slip ...
• turbidite
  A sequence of sediment or rock deposited from, or inferred to have been deposited from, a turbidity current. It is characterized ...
• platform
  i. The place on top of a breaker where the freshly mined coal is weighed by a weigh boss just before it is dumped into the ...
• adverse
  To oppose the granting of a patent to a mining claim.
• stretch
  A particular direction or course; as, the stretch of a coal seam. Ref: Standard, 2
• turbidity current
  A density current in water, air, or other fluid, caused by different amounts of matter in suspension, such as a dry-snow ...
• stretched-pebbles
  Stretched-pebbles are conglomerates made up of clasts of any size that have been aligned by processes that occurred after ...
• wilbur
  In fine mineral collecting, a wilbur is an informal collector’s term for a tiny, often nearly microscopic imperfection on an ...
• disharmonic folding
  Folding in which there is an abrupt change in fold profile when passing from one folded surface or layer to another. It is ...
• harmonic folding
  Folding in which the strata remain parallel or concentric, without structural discordances between them, and in which there are ...
• nappe
  i. A sheetlike, allochthonous rock unit, which has moved on a predominantly horizontal surface. The mechanism may be thrust ...
• thrust sheet
  The body of rock above a large-scale thrust fault whose surface is horizontal or very gently dipping. Synonym of: thrust ...
• décollement
  Detachment structure of strata owing to deformation, resulting in independent styles of deformation in the rocks above and below. ...
• ptygmatic folding
  Primary chaotic, random and disconnected folding in migmatites (injection gneisses, etc.), caused by the high-temperature and ...
• mesosome
  The unmodified, older host rock portion of a migmatite that has largely resisted partial melting, i.e. the unchanged host ...
• plate tectonics
  A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is ...
• tectonic plate
  A torsionally rigid thin segment of the Earth's lithosphere, which may be assumed to move horizontally and adjoins other ...
• epimorph
  A hollow shell, or mold, left by a mineral that had overgrown an initial mineral which has dissolved away. See also ...
• perimorph
  A crystal or aggregate of one mineral species enclosing one of another mineral species. An endomorph is the inner mineral ...
• shatter cone
  Shatter cones are geological features comprising cone-like radiating grooves or stria that are only known to form in the bedrock ...
• endomorph
  A crystal surrounded by another crystal of a different mineral species. Adj. endomorphic, endomorphous. See also perimorph.
• polymorph
  A mineral whose crystal structure is different from another mineral of identical chemical composition. For example, Al^2(SiO^4)O ...
• pseudomorph
  A mineral sample with the external crystal form of one mineral and the internal chemistry of another; e.g., cubes of goethite ...
• train
  A number of empty or loaded mine cars, coupled together, for transport by rope haulage or locomotive. See Also: journey