Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.

Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g., as iron ores, pigments, catalysts, in thermite (see the diagram), Hemoglobin. Common rust is a form of iron(III) oxide. Iron oxides are widely used as inexpensive, durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy" end of the yellow/orange/red/brown/black range.

Oxides

 * iron(II) oxide, wüstite (FeO)
 * iron(II,III) oxide, magnetite (Fe3O4)
 * [iron(II,III) oxide], (Fe4O5)
 * iron(III) oxide (Fe2O3)
 * alpha phase, hematite (α-Fe2O3)
 * beta phase, (β-Fe2O3)
 * gamma phase, maghemite (γ-Fe2O3)
 * epsilon phase, (ε-Fe2O3)

Hydroxides

 * iron(II) hydroxide (Fe(OH)2)
 * iron(III) hydroxide (Fe(OH)3), (bernalite)

Oxide/hydroxides

 * goethite (α-FeOOH),
 * akaganéite (β-FeOOH),
 * lepidocrocite (γ-FeOOH),
 * feroxyhyte (δ-FeOOH),
 * ferrihydrite (Fe5HO8·4H2O approx.), or 5Fe2O3•9H2O, better recast as FeOOH•0.4H2O


 * high-pressure FeOOH
 * schwertmannite (ideally Fe8O8(OH)6(SO)·nH2O or Fe3+16O16(OH,SO4)12-13·10-12H2O)
 * green rust (FeIIIxFeIIy(OH)3x+2y-z(A-)z; where A- is Cl- or 0.5SO42-)

Microbial degradation
Shewanella oneidensis reduces iron oxide in anaerobic conditions by breathing the oxygen molecules.