Calcium carbonate is available in nature in the form of 

• Calcium carbonate, chemically written as ${\mathrm{CaCO}}_3$ is found commonly in rocks in the form of minerals. It is used as a dietary supplement to maintain the calcium deficiency in the body. It is also used as an antacid to provide relief from indigestion.  

Naturally, calcium carbonate is found in the form of limestone, marbles, calcite (chalk) as well as skeletons of corals. Pumice stone is made from calcium carbonate.