is a soft, silvery-white metallic element found most widely in such rocks as chalk, limestone, and marble. It is the fifth most abundant element on Earth, making up about 3½ per cent of the Earth's crust. The name calcium comes from calx, or lime (an oxide of calcium).

Sir Humphry Davy, an English chemist, first isolated calcium as a pure metal in 1808. However, the ancient Egyptians, Greeks, and Romans knew about calcium compounds and used them to make mortar.

Chemical Properties

Calcium is one of the Alkaline Earth Metals. It has an atomic number of 20 and an atomic weight of 40.08. Calcium melts at 839° C and boils at 1,484°. It has a specific gravity of 1.55.

Sources

Calcium reacts readily with both oxygen and water. In nature, therefore, it occurs only in compounds -- primarily as calcium carbonate, calcium fluoride, and calcium sulfate. Pure calcium metal, used in certain kinds of alloys, is obtained from molten calcium chloride through a process called electrolysis.

Uses

Various industrial processes, such as leather tanning and petroleum refining, involve calcium oxide. Calcium fluoride and calcium sulfate are used in making cement and plaster for construction work. Manufacturers use other calcium compounds in a wide variety of products ranging from fertilizer to paint.

Calcium is essential to all living things, especially human beings and other animals. It is vital for the growth and maintenance of the bones and teeth, and it helps the blood to clot and the muscles to contract.

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