Calcium carbonate

From Environmental Technology

Calcium Carbonate (Calcite) is one of the most abundant minerals on the Earth's surface. It's more commonly found in Limestone and it is also the primary mineral in Metamorphic Marble. It also collects in hot springs, and occurs in caverns as Stalactites and Stalagmites. Calcite is often found in the shells of marine life (i.e. Plankton, Bivalves, etc.).

[edit] Reference:

http://en.wikipedia.org/wiki/Calcite