calcite


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calcite

(kăl`sīt), 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 sparIceland spar,
colorless variety of crystallized calcite, characterized by its properties of transparency and double refraction. It is used chiefly in the manufacture of Nicol prisms, which are essential parts of polarizing microscopes and other optical instruments.
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 is clear, transparent calcite. Other important forms of the mineral are limestonelimestone,
sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine.
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, marblemarble,
metamorphic rock composed wholly or in large part of calcite or dolomite crystals, the crystalline texture being the result of metamorphism of limestone by heat and pressure.
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, chalkchalk,
mineral of calcium carbonate, similar in composition to limestone, but softer. It is characteristically a marine formation and sometimes occurs in great thickness; the chief constituents of these chalk deposits are the shells of minute animals called foraminiferans.
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, marlmarl
or bog lime,
soil, essentially clay mixed with carbonate of lime, highly valued as a dressing or fertilizer. It crumbles rapidly and easily. Marl in which the lime is in the form of invertebrate shells is called shell marl.
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, stalactite and stalagmitestalactite and stalagmite
, mineral forms often found in caves; sometimes collectively called dripstone. A stalactite is an icicle-shaped mass of calcite attached to the roof of a limestone cavern.
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 formations, travertinetravertine
, form of massive calcium carbonate, CaCO3, resulting from deposition by springs or rivers. It is often beautifully colored and banded as a result of the presence of iron compounds or other (e.g., organic) impurities.
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, and Oriental alabasteralabaster,
fine-grained, massive, translucent variety of gypsum, a hydrous calcium sulfate. It is pure white or streaked with reddish brown. Alabaster, like all other forms of gypsum, forms by the evaporation of bedded deposits that are precipitated mainly from evaporating
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. 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 smeltingsmelting,
in metallurgy, any process of melting or fusion, especially to extract a metal from its ore. Smelting processes vary in detail depending on the nature of the ore and the metal involved, but they are typified in the use of the blast furnace.
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 and as a soil conditioner.

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

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.

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.

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)
References in periodicals archive ?
2+]]Caicite) to bring the water sample point into calcite equilibrium curve.
The mineralogy of ooids is usually either calcite or aragonite, which correspond to climatic greenhouse and icehouse conditions: being able to distinguish the two is important in interpreting the environmental significance of a particular rock formation.
3, 4A, and 5), the calcium K[alpha] intensity of the calcite layer is close to that of crystalline calcite of mollusc shell, used as a standard (Fig.
RS is the ratio of calcite activity product (Ka) to calcite solubility product (Ksp), SI value of less than 1 indicates undersaturation, SI of 1 indicates saturation, and SI of more than 1 indicates supersaturation.
The GCC pigment showed broad particle size distribution (BPSD), while the calcite PCC of rhombohedral habit (PCC1) and the aragonite PCC of orthorhombic habit (PCC2) showed quite narrow particle size distribution (NPSD).
The light enters the calcite and splits into two rays of different polarisations travelling at different speeds and in different directions.
Samples of calcite were taken from columns A and B to establish a chronological context for the Lene Hara petroglyphs using U/Th determinations, reported with 2 sigma errors and shown in Table 1.
Fillers, namely calcite and silica were loaded as 10, 20, and 30 phr in the composites.
Evidence of Calcite Precipitation Induced Bacillus Pasteurii
The froth from these experiments was floated again using the same procedure to ensure full recovery of the oil shale from calcite.
But rainwater can penetrate into some of the older mounds and wash through high levels of calcite.