|CALCITE MINERAL FACTS|
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Calcite Mineral Facts:
Chemical Formula: CaCO3
Colors: Colorless and when pure, but often colored by impurities. May be variously tinted, gray, red, green, blue, yellow, or even brown to black when very impure
Cleavage: Perfect cleavage parallel to unit rhombohedron (angle of rhombohedron = 105 and 75). The cleavage of calcite is so perfect that crystals when shattered by a hammer blow usually break into perfect little rhombohedrons.
Crystallography: Hexagonal - Rhobohedral
Luster:. Vitreous to earthy.
Optics: (Refractive Index): Transparent to opaque. RI: w = 1.658; E = 1.486; Strong Double Refraction
Structure and Associated Minerals:
Theoretically, calcite contains 56 per cent CaO and 44 per cent CO2, but practically the mineral contains also small quantities of Mg, Fe, Mn, Zn and Pb, metals whose carbonates are isomorphous with Calcite. It is a very poor conductor of electricity.
The principal varieties of the mineral to which distinct
names have been given are:
Calcite, Fine Crystals
Identification and Diagnostics
Localities and Origins:
Calcite is doubly refractive, splitting light in two.
Calcite has many important uses. In the form of Iceland spar, on account of its strong double refraction, it is employed in optical instruments for the production of polarized light. Calcite rocks are used as building and ornamental stones. Marbles are used very extensively as ornamental and building material. The most important marble quarries in the United States are found in Vermont, New York, Georgia, Tennessee, etc. Calcite is also employed as fluxes in smelting operations, as one of the ingredients in glass-making and in the manufacture of lime, and certain ground improving fertilizers. The most important use for calcite is for the manufacture of lime for mortars and cements. Limestone when heated to about 1000 F. loses its carbonic acid, and is converted into quicklime, CaO. This, when mixed with water (staked lime), swells, gives off much heat, and finally by absorption of carbon dioxide from the air hardens, or, as commonly termed, "sets." The chemistry of the process of their hardening is not fully understood, but various silicates of calcium and aluminium are probably formed.
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Green calcite, showing cleavage lines
Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.
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