Iron(II,III) oxide is the chemical compound with formula Fe
3O
4. It occurs in nature as the mineral
magnetite. It is one of a number of
iron oxides, the others being
iron(II) oxide (FeO), which is rare, and
iron(III) oxide (Fe
2O
3) also known as
hematite. It contains both Fe
2+ and Fe
3+ ions and is sometimes formulated as FeO · Fe
2O
3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is
ferrimagnetic, but is sometimes incorrectly described as
ferromagnetic. Its most extensive use is as a black pigment which is synthesised rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.