It is impossible to specify all the important districts for the occurrence of calcite in its various forms. Uses - The most important use for calcite is for the manufacture of cements and lime for mortar. Limestone when heated to about 900 degrees C forms CaO. The CaO, when mixed with water, forms slaked lime that swells, gives off heat, and hardens or sets. Portland cement is most widely produced type of cement. Small amounts of magnesium carbonate and iron oxide are also present.
Limestone is also a raw material for the chemical industry and is utilized as a soil conditioner.
Great quantities are quarried each year as a flux for smelting various metallic ores and as road construction material. Calcite in several forms is used in the building industry. Limestone and marble as dimension stone are used both for construction purposes and for decorative exterior facings. Polished slabs of travertine and Mexican onyx are commonly used as ornamental stone. The most important marble quarries are in Vermont, New York, Georgia, and Tennessee.