Limestone
A sedimentary rock type composed of mostly calcium carbonate, that formed by chemical precipitation from sea water or by accumulation of fossils with carbonate shells.
Limestone can be created by clastic and non-clastic processes. Clastic limestones are formed from the break up and deposition of shells, coral and other marine organisms by wave-action and ocean currents. Non-clastic limestones can be formed either as a precipitate or by the lithification of coral reefs, marine organism shells, or marine organism skeletons.