calcium

A silvery, moderately hard metallic element that constitutes approximately 3 percent of the earth's crust and is a basic component of most animals and plants. It occurs naturally in limestone, gypsum, and fluorite, and its compounds are used to make plaster, quicklime, Portland cement, and metallurgic and electronic materials. Atomic number 20; atomic weight 40.08; melting point 842 to 848°C; boiling point 1,487°C; specific gravity 1.55; valence 2. See Table at element.