Iron(II) oxide

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Iron(II) oxide
Iron(II) oxide
CAS number 1345-25-1 YesY
PubChem 14945
ChemSpider 14237 YesY
UNII G7036X8B5H YesY
ChEBI CHEBI:50820 YesY
Jmol-3D images Image 1
Molecular formula FeO
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 in water Insoluble
Solubility insoluble in alkali, alcohol
dissolves in acid
Refractive index (nD) 2.23
EU Index Not listed
Main hazards can be pyrophoric
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity (yellow): no hazard code Special hazards (white): no codeNFPA 704 four-colored diamond
Autoignition temperature variable
Related compounds
Other anions iron(II) fluoride, iron(II) sulfide, iron(II) selenide, iron(II) telluride
Other cations manganese(II) oxide, cobalt(II) oxide
Related compounds Iron(III) oxide, Iron(II,III) oxide
Infobox references

Iron(II) 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, 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.[2]


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

FeC2O4 → FeO + CO2 + CO

The procedure is conducted a protective atmosphere to avoid the formation of ferric oxide. A similar procedure can also be used for the synthesis of manganous oxide and stannous oxide.[3][4]

Stoichiometric FeO can be prepared by heating Fe0.95O with metallic iron at 770 °C and 36 kbar.[5]


FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe3O4:[2]

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.[5]

Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.[5]

Occurrence in nature[edit]

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.[6]


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 for filtering phosphates from home aquaria.


  3. ^ 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.
  4. ^ Practical Chemistry for Advanced Students, Arthur Sutcliffe, 1930 (1949 Ed.), John Murray - London
  5. ^ a b c Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford University Press ISBN 0-19-855370-6
  6. ^ Science Jan 2012

External links[edit]