
Limestone - (Calcium Carbonate) Limestone by definition contains at least 50% calcium carbonate by weight. A sedimentary rock formed by a chemical transformation in relation to various organisms such as coral, algae, and bivalves. Also formed as a carbonate precipitate around small particles in water (eg. Indiana Oolitic Limestone), or is deposited by waters rich in calcium carbonate (Travertine). Fossils are often visible in Limestone.