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Rust is the oxide that is formed by open-air oxidation of iron. The chemical composition of rust is mainly iron(III) oxide (Fe<sub>2</sub>O<sub>3</sub>), and under wet conditions may include iron(III) oxide-hydroxide (FeO(OH)). Rusting is the common term for corrosion of iron and its alloys, such as steel. Although oxidation of other metals is equivalent, these oxides are not commonly called rust.