Calcium is named from the Latin calx, lime and was first prepared by the Romans in the first century under the name calx. The metal was actually discovered in 1808. Calcium is a metallic element, fifth in abundance in the earth's crust, of which it comprises more than 3%. It is never found in nature uncombined, it occurs abundantly as limestone, gypsum and fluorite. The metal has a silvery color, is rather hard and is prepared by electrolysis. The metal is used as a reducing agent in preparing other metals such as thorium, uranium and zirconium; and is used as a deoxidizer, desulfurizer or decarburizer for various ferrous and nonferrous alloys. It is an essential part of leaves, bones, teeth and shells.