Calcium is a chemical element, a member of the alkaline-earth metals group, represented by the atomic symbol Ca and the atomic number 20. It has an atomic weight of 40.08. In its pure form, calcium is a silvery-white metal, although it is never found in this free state naturally. It is, however, one of the most abundant substances on Earth, comprising approximately 3.64 percent of the Earth's crust. Pure calcium metal has a melting point of 1547.6 ° F (842 ° C) and boils at 2703 ° F (1484 ° C). It is used in several industries, including glass, battery, and steel production. It also combines readily with many other elements, and these compounds are used as well for a variety of purposes.

Calcium was not known as an element until the early 1800s, when chemists, trying to prove the existence of unknown metals in natural compounds, began using the newly discovered phenomenon of electricity...