Iron(II) oxide is the
inorganic compound with the formula FeO. Its mineral form is known as
wüstite. One of several
iron oxides, it is a black-colored powder that is sometimes confused with
rust, which consists of hydrated
iron(III) oxide (ferric oxide). Iron(II) oxide also refers to a family of related
non-stoichiometric compounds, which are typically iron deficient with compositions ranging from Fe
0.84O to Fe
0.95O.