A common name for iron oxide is iron (III) oxide or rust. The chemical formula for this substance is Fe2O3. However, there are other compounds that consist of oxygen and iron, such as magnetite, which has the formula Fe3O4.
Iron (III) oxide is the reaction between the metal iron and excess oxygen found in air. The balanced chemical equation for this reaction is 4Fe(s) + 3O2(g) produces 2Fe2O3(s), where "s" stands for solid and "g" is gas. Hematite, which is a mineral found in nature, also has this same formula. Hematite is reddish in appearance.
Magnetite is another mineral formed in nature and is black in color. The formation of Fe3O4 occurs when iron is heated in the presence of small amounts of oxygen.