Calcium Carbonate, a compound of calcium, carbon, and oxygen. A number of common rocks (such as limestone and marble) and minerals (such as calcite and travertine) are largely made up of this compound, as are pearls, coral, and a number of sea shells. Calcium-carbonate rocks and minerals are used in building construction and in the manufacture of iron, steel, soda, cement, and glass. They are also used for treating acid soils. When calcium carbonate is heated, it decomposes into lime and carbon dioxide. Both of these compounds are important in industry.

Pure calcium carbonate is a soft, white, insoluble powder. In its pure form it is often called precipitated chalk, and is used as a polishing powder, as in tooth powder. Calcite is the mineral form of calcium carbonate. It often occurs in fine-grained form as oriental alabaster, also called onyx marble; in compact or porous form as travertine; and in colorless, transparent crystals as Iceland spar.

Chemical formula: CaCO3.