The most common and most useful metallic element, being of almost universal occurrence, usually in the form of an oxide (as hematite, magnetite, etc), or a hydrous oxide (as limonite, turgite, etc). It is reduced on an enormous scale in three principal forms; viz, cast iron, steel, and wrought iron. Iron usually appears dark brown, from oxidation or impurity, but when pure, or an fresh surface, is a gray or white metal. It is easily oxidized (rusted) by moisture, and is attacked by many corrosive agents. Symbol Fe (Latin Ferrum). Atomic weight 55.9. Specific gravity, pure iron.86; cast iron.