Iron oxides are compounds that are composed of iron and oxygen. There are seventeen known iron oxides and oxyhydroxides, of which the best known is rust, a type of iron oxide. Iron oxides and oxyhydroxides are common in nature and play a significant role in many processes, both geological and biological. Iron oxide, or black iron oxide, is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron oxide (Fe2O3) which also occurs naturally as the mineral hematite They are used as iron ores, pigments, catalysts, and in thermite, and occur in hemoglobin. Iron oxides are inexpensive and durable pigments in paints, coatings and colored concretes. Colors commonly available are in the “earthy” end of the yellow/orange/red/brown/black range.