Iron is the chemical element that forms the main metallic component of rust together with oxygen.
Rust is not a single pure compound in every situation; it is a mixture of hydrated iron oxides and hydroxides formed when iron reacts with oxygen and water. The process is called corrosion. Salt and acidic conditions can speed it up because they help electrical and chemical reactions proceed on the metal surface.
Iron has atomic number 26 and the symbol Fe, derived from the Latin ferrum. It is one of the most widely used metals because it is strong, abundant, and useful in alloys such as steel. Pure iron is relatively soft, while steel gains different properties from carbon and other elements.
A common mistake is to call every reddish corrosion product rust. Copper develops a green patina, while aluminum forms a thin protective oxide layer. Iron rust is especially damaging because it can flake away and expose fresh metal beneath.