The chalk is the remains of the shells of marine microorganisms that died and sank to the bottom of the ancient seas. It oxidizes in moist air and the surface becomes coated with calcium oxide, hyrdroxide and carbonate. This makes it the 5th most abundant in the earth's crust and the third most abundant metal. Calcium metal is prepared by electrolysis of molten calcium chloride. Calcium is used primarily in the form of lime in steelmaking.
Slaked lime is an important material to control air pollution.
Lime is also important as a raw material in chemical manufacture, water treatment, papermaking and as concrete in the construction industry. The largest use of plaster of Paris is in the building industry as wall plasters and wall boards. It is used for architectural decorations and in the medical field for the setting of broken bones. In addition it is used as moulds in the production of ceramics and of metallic jewellry. Calcium is also presence in our bodies.