Calcium is a silver-white light metal. It oxidizes in moist air and the surface becomes coated with calcium oxide, hyrdroxide and carbonate. Discovered in 1808, calcium makes up of about 3.4 % of the earth's crust. This makes it the 5th most abundant in the earth's crust and the third most abundant metal.

Large amounts of calcium are found in:

• the mineral, dolomite, MgCO₃.CaCO₃,
• minerals of calcium carbonate, CaCO₃, like limestone, deposits of marl, chalk, marble, calcite, and aragonite (Calcium carbonate also occurs in other natural forms such as marine animal shells and pearls.),
• the mineral, gypsum, CaSO₄.2H₂O,
• the mineral, fluorite, CaF₂, and
• boiler scale, an extremely hard incrustation of calcium and magnesium compounds, usually insoluble carbonates and sulfates. It forms on the inner surfaces of boilers where "hard" water has been in contact with them for long periods of time.

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.

Plaster of Paris is calcium sulphate hemihydrate ( (CaSO₄)₂.H₂O ). 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. In an adult, there is about 1 kg calcium in the teeth and bones. Calcium also plays a role in regulating heartbeat.