An Etymological Dictionary of Astronomy and Astrophysics

A metallic chemical element; symbol Ca. → Atomic number 20; → atomic weight 40.08; → melting point about 839°C; → boiling point 1,484°C; → specific gravity 1.55 at 20°C; → valence +2. It is fifth in abundance in the Earth’s crust, of which it forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells. Never found in nature uncombined, it occurs abundantly as limestone, gypsum, and fluorite. Calcium has several radioactive isotopes. It was first isolated by the British chemist Humphry Davy in 1808.

See also: Coined by Sir Humphry Davy from L. calx (genitive calcis) “lime (CaO) or limestone (CaCO₃)” in which it was found, from Gk. khalix “small pebble,” see also → calculate, + → -ium.