Calcium

Calcium is the fifth most common element in Earth's crust and the most common metal in the human body, where it builds bones and teeth. As a pure metal it is soft, silvery and reacts with water, so in nature it is always combined, most often as calcium carbonate in limestone, chalk, marble and seashells. Humphry Davy first isolated it in 1808.

Industry uses calcium mostly as compounds. Limestone is heated to make lime, or calcium oxide, for cement and for soda-lime glass. Limestone is also added to blast furnaces, where it soaks up impurities as slag on the way to pig iron and steel.