Iron(II) oxide
Iron(II) oxide
IUPAC name
Iron(II) oxide
Other names
Ferrous oxide,iron monoxide
3D model (JSmol)
ECHA InfoCard 100.014.292 Edit this at Wikidata
  • InChI=1S/Fe.O checkY
  • InChI=1/Fe.O/rFeO/c1-2
  • [Fe]=O
Molar mass 71.844 g/mol
Appearance black crystals
Density 5.745 g/cm3
Melting point 1,377 °C (2,511 °F; 1,650 K)[1]
Boiling point 3,414 °C (6,177 °F; 3,687 K)
Solubility insoluble in alkali, alcohol
dissolves in acid
+7200·10−6 cm3/mol
Occupational safety and health (OHS/OSH):
Main hazards
can be combustible under specific conditions[2]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
200 °C (392 °F; 473 K)
Safety data sheet (SDS) ICSC 0793
Related compounds
Other anions
Iron(II) sulfide
Iron(II) selenide
Iron(II) telluride
Other cations
Manganese(II) oxide
Cobalt(II) oxide
Related Iron oxides
Iron(II,III) oxide
Iron(III) oxide
Related compounds
Iron(II) fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite.[3][4] 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.[5]


FeO can be prepared by the thermal decomposition of iron(II) oxalate.

FeC2O4 → FeO + CO2 + CO

The procedure is conducted under an inert atmosphere to avoid the formation of iron(III) oxide (Fe2O3). A similar procedure can also be used for the synthesis of manganous oxide and stannous oxide.[6][7]

Stoichiometric FeO can be prepared by heating Fe0.95O with metallic iron at 770 °C and 36 kbar.[8]


FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe3O4:[5]

  • 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.[8]

In contrast to the crystalline solid, in the molten state iron atoms are coordinated by predominantly 4 or 5 oxygen atoms.[9]

Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.[8][10]

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.[11]


Iron(II) oxide is used as a pigment. It is FDA-approved for use in cosmetics and it is used in some tattoo inks. It can also be used as a phosphate remover from home aquaria.

See also


  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ "404 - School of Art & Design" (PDF). ((cite web)): Cite uses generic title (help)
  3. ^ "Wüstite".
  4. ^ "List of Minerals". March 21, 2011.
  5. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  6. ^ 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.
  7. ^ Practical Chemistry for Advanced Students, Arthur Sutcliffe, 1930 (1949 Ed.), John Murray - London
  8. ^ a b c Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford University Press ISBN 0-19-855370-6
  9. ^ Shi, Caijuan; Alderman, Oliver; Tamalonis, Anthony; Weber, Richard; You, Jinglin; Benmore, Chris (2020). "Redox-structure dependence of molten iron oxides". Communications Materials. 1 (1): 80. Bibcode:2020CoMat...1...80S. doi:10.1038/s43246-020-00080-4.
  10. ^ Proceedings of the 5th Unconventional Resources Technology Conference. Tulsa, OK, USA: American Association of Petroleum Geologists. 2017. doi:10.15530/urtec-2017-2670073. ISBN 978-0-9912144-4-0.
  11. ^ "Science Jan 2012". Archived from the original on January 24, 2012.