limestone
Limestone, one of the three sedimentary rocks, is made in oceans and seas. It is formed in two steps. First, a sediment, such as sand, is deposited along with calcium carbonate, and then is compacted. Then the water is squeezed out of it and it becomes limestone. A unique characteristic of limestone is the way it fizzes in acid. It does this because it contains calcium carbonate. When acid reacts with calcium carbonate, carbon dioxide is given off. If a rock fizzes when you put acid on it, it probably contains some limestone in it. When animals die, their bones, shells and scales that have calcium settle to the bottom of the ocean and can be put into forming the rock. Calcium carbonate made by animals exhaling CO2 and calcium in the water sinks to the bottom of the sea or ocean. It forms a layer on the bottom and now can turn into limestone. The main component in limestone that makes it fizz is either shells or coral.