Iron(II) oxide or ferrous 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, the latter of 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 Fe0.84O to Fe0.95O.
Ferrous oxide,iron monoxide
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||71.844 g/mol|
|Melting point||1,377 °C (2,511 °F; 1,650 K)|
|Boiling point||3,414 °C (6,177 °F; 3,687 K)|
|Solubility||insoluble in alkali, alcohol |
dissolves in acid
Refractive index (nD)
|Main hazards||can be combustible under specific conditions|
|Safety data sheet||ICSC 0793|
|NFPA 704 (fire diamond)|
|iron(II) fluoride, iron(II) sulfide, iron(II) selenide, iron(II) telluride|
|manganese(II) oxide, cobalt(II) oxide|
|Iron(III) oxide, Iron(II,III) oxide|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
FeO can be prepared by the thermal decomposition of iron(II) oxalate.
- FeC2O4 → FeO + CO2 + CO
FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe3O4:
- 4FeO → Fe + Fe3O4
Iron(II) oxide adopts the cubic, rock salt structure, where iron atoms are octahedrally coordinated by oxygen atoms and the oxygen atoms octahedrally coordinated by iron atoms. The non-stoichiometry occurs because of the ease of oxidation of FeII to FeIII effectively replacing a small portion of FeII with two thirds their number of FeIII, which take up tetrahedral positions in the close packed oxide lattice.
Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.
Occurrence in nature
Iron(II) oxide makes up approximately 9% of the Earth's mantle. Within the mantle, it may be electrically conductive, which is a possible explanation for perturbations in Earth's rotation not accounted for by accepted models of the mantle's properties.
- Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- H. Lux "Iron (II) Oxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1497.
- Practical Chemistry for Advanced Students, Arthur Sutcliffe, 1930 (1949 Ed.), John Murray - London
- Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford University Press ISBN 0-19-855370-6
- Science Jan 2012 Archived January 24, 2012, at the Wayback Machine