Iron(III) oxide or
ferric oxide is the
inorganic compound with the formula Fe
2O
3. It is one of the three main
oxides of
iron, the other two being
iron(II) oxide (FeO), which is rare, and
iron(II,III) oxide (Fe
3O
4), which also occurs naturally as the mineral
magnetite. As the mineral known as
hematite, Fe
2O
3 is the main source of iron for the steel industry. Fe
2O
3 is
ferromagnetic, dark red, and readily attacked by acids. Iron(III) oxide is often called
rust, and to some extent this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered an ill-defined material, described as
hydrated ferric oxide.