one of the commonest minerals, calcium carbonate, CaCO 3 , found in a great variety of crystalline forms: a major constituent of limestone, marble, and chalk; calc-spar.
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)