Limestone is a hard, durable sedimentary rock. It is formed from the mineral calcite, which is made from calcium carbonate. Limestone is found in shallow, warm sea beds and lakes. It forms through an accumulation of marine life, such as coral, shells and other organic ocean debris. It can also form through a process of chemical precipitation of calcium carbonate directly from the water in which it is found. Limestone is abundant in warm, shallow marine water throughout the world.