calcite

calcite

calcite (kălˈsīt), very widely distributed mineral, commonly white or colorless, but appearing in a great variety of colors owing to impurities. Chemically it is calcium carbonate, CaCO₃, but it frequently contains manganese, iron, or magnesium in place of the calcium. It crystallizes in the hexagonal system, its crystals being characterized by highly perfect cleavage. Calcite also occurs in a number of massive forms, in which it may be coarsely to finely granular (as in marble), compact (as in limestone), powdery (as in chalk), or fibrous. One crystalline form, called dogtooth spar because of its dogtooth appearance, exhibits faces of perfect scalene triangles. Another form, satin spar, is finely fibrous and has a satin luster. Iceland spar is clear, transparent calcite. Other important forms of the mineral are limestone, marble, chalk, marl, stalactite and stalagmite formations, travertine, and Oriental alabaster. Millions of tons of calcite, in the form of limestone and marble, are mined annually. Besides its use as a building stone, it is the raw material for quicklime and cement, and is used extensively as a flux in smelting and as a soil conditioner.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Calcite

 

(calcareous spar), a mineral with chemical composition CaCO₃, containing 56 percent CaO and 44 percent CO₂ and frequently Mg, Fe, Mn (up to 8 percent) as well as Zn, Co, Sr, and Ba. Calcite crystallizes in the trigonal system. It exists in the form of crystals with various habits—rhombohedral, scalenohedral, prismatic, or tabular—as well as in the form of stalactites and solid, granular, and earthy masses (chalk). The Ca and C atoms in the calcite structure are arranged at the lattice points of the rhombohedral lattices as though pushed into one another. The O atoms are in groups of three around each C atom and lie in the same plane. Calcite is brittle and exhibits perfect cleavage on the rhombohedron [1011]. Twins are a characteristic feature. Calcite crystals exhibit a high birefringence, and many are strongly fluorescent. Calcite’s hardness on the mineralogical scale is 3 and its density, 2, 720-2, 800 kg/m³. When heated, calcite decomposes at a temperature of 825°C; it is readily soluble in acids.

Calcite is one of the most widely distributed minerals in the earth’s crust, particularly among the hydrothermal formations in contact metasomatic deposits and in amygdaloids and geodes of igneous rocks. It is sometimes formed under magmatogenic conditions, producing carbonatites. Calcite precipitates from hot calcareous springs in the form of tufa (travertine). Enormous masses of calcite are formed as deposits in ocean basins, partly by biogenesis. Calcite appears as the main constituent of limestone, marble, and other sedimentary and metamorphic rocks widely used as construction and facing materials. Pure and transparent varieties of calcite—for example, Icelandic spar—are used in the optics industry.

REFERENCES

Opticheskie materialy dlia infrakrasnoi tekhniki.Moscow, 1965.
“Kal’tsit.” In Fizicheskii entsiklopedicheskii slovar’, vol. 2. Moscow, 1962.
Kostov, I. Mineralogiia. Moscow, 1971. (Translated from English.)

M. D. DORFMAN and M. O. KLIIA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

calcite

[′kal‚sīt]

(mineralogy)

CaCO₃ One of the commonest minerals, the principal constituent of limestone; hexagonal-rhombohedral crystal structure, dimorphous with aragonite. Also known as calcspar.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

calcite

A mineral form of calcium carbonate; the principal constituent of limestone, chalk, and marble; usually a major raw material used in portland cement manufacture.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

calcite

a colourless or white mineral (occasionally tinged with impurities), found in sedimentary and metamorphic rocks, in veins, in limestone, and in stalagmites and stalactites. It is used in the manufacture of cement, plaster, paint, glass, and fertilizer. Composition: calcium carbonate. Formula: CaCO₃. Crystal structure: hexagonal (rhombohedral)

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005