There are a number of iron oxides:

Iron oxides

• Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites.

• Iron(III) oxide or ferric oxide (Fe₂O₃) known in its natural state as hematite or haematite, but also purified for use as a coating in magnetic audio and computer media, where it is known as ferric oxide. Also known as rouge.

• Iron(II,III) oxide or ferrous ferric oxide (Fe₃O₄), better known as the black-coloured mineral magnetite or lodestone also seen on mars

. .

Iron hydroxides

• Iron(II) hydroxide Fe(OH)₂. green colour.

• Iron(III) hydroxide FeO(OH) found as the mineral goethite. Red-brown colour. Also found as the minerals siderogel and feroxyhyte. There is a variant known as lepidocrocite.

• Iron(III) hydroxide Fe(OH)₃. Dark brown.

There are also several other variants.

See also

A number of these compounds are found in rust and rusticles.