Iron(II,III) oxide is the chemical compound with formula Fe₃O₄. 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 (Fe₂O₃) also known as hematite. It contains both Fe²⁺ and Fe³⁺ ions and is sometimes formulated as FeO · Fe₂O₃. 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.