Limestone types may be formed either inorganically or biochemically and include coral reefs, chalks, coquina and oolitic limestone. Limestone is composed of calcite and makes up approximately 10 percent of all sedimentary rocks.
Limestone is found in many parts of the world, both on land and in water, including Central America and England. Numerous conditions exist to produce many types of limestone. The skeletons of invertebrate animals make up limestone originating from coral reefs. Algae that live within the reefs secrete calcium carbonate to seal the structures of the organisms together, helping to form the hardened structures.
Chalk is an example of a biochemically produced limestone. It is produced from the skeletal parts of marine organisms. Poorly cemented shells and shell fragments produce the limestone that is known as coquina.
Caves contain inorganic limestone sources known as stalactites and stalagmites. Calcium carbonate, that is dissolved in water, forms limestone that is often referred to as dripstone. Oolitic limestone is another type of limestone that is inorganic. It is formed from spherical grains called ooids. Small particles that are suspended on shallow marine waters are where these grains form. Calcium carbonate is present in the water and forms in layers, contributing to the limestone formations.