Limestones
Limestones are made up largely of calcite (calcium carbonate) as their main mineral. Limestones fizz when a drop of dilute hydrochloric acid is placed on them. Uses of Limestone.
Shelly limestone
Shelly limestone is made up of the shells and skeletons of invertebrates that live in the sea (or sometimes in fresh water). The shells are not usually whole, as they are broken up by waves.
Oolitic limestone
Oolitic limestone is made up of small spheres called ooiliths that are stuck together by lime mud. They form when calcium carbonate is deposited on the surface of sand grains rolled (by waves) around on a shallow sea floor.
Chalk
Chalk is a soft, white limestone, made up of the microscopic remains (coccoliths) of tiny planktonic organisms, that live in the surface waters of tropical seas. The inset photo was taken using an electron microscope.
