Calcium Carbonate

n. white chemical compound found in nature as chalk or calcite or limestone

Calcium carbonate is a chemical compound, with the chemical formula CaCO3. It is a common substance found as rock in all parts of the world, and is the main component of shells of marine organisms, snails, and eggshells. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid.
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Calcium carbonate n. A calcium salt used as a dietary supplement and as an antacid. calcium carbonate Adcal, Alka-Mints, Cacit, Calcarb 600, [more]Calcium carbonate - Community and Resources

Noun
1. a salt found in nature as chalk or calcite or aragonite or limestone
(hypernym) carbonate
(hyponym) dripstone
(substance-holonym) chalk

A mineral taken primarily as a supplement to prevent osteoporosis. It is also being studied for cancer prevention.