Iron, a chemical element, symbol Fe; for physical constants see Periodic Table. Iron has been used since prehistoric times. It is the fourth most abundant element on earth. The earth's core is thought to be composed mainly of iron. It is found in nature as the minerals hematite, magnetite, limonite, siderite, and taconite. It is a major component of some meteorites. Iron is prepared by reduction of its oxides with carbon in a reverberatory furnace. Iron is a silvery-white, soft, malleable, ductile, magnetic, metal. The commercial metal appears in three forms: cast iron, wrought iron, and steel. Iron is used to produce many important alloys, particularly steels. Nickel, chromium (stainless), tungsten, molybdenum, manganese, and aluminum steels being the most widely used. Compounds of iron are used in inks, pigments, mordants, water purification, and medicine. It is essential to plant and animal life. Iron is the most important of all metals.