Ferrous chromite, FeO.Cr₂O₃

Ferrous chromite, FeO.Cr₂O₃, occurs in nature as chromite. It may be prepared in the laboratory by heating to a high temperature an intimate mixture of iron filings, ferrous carbonate, and potassium bichromate, covered with a thin layer of cryolite. The cooled product is extracted with water and concentrated acids in succession; a residue is obtained containing chromite as small octahedra, cubo-octahedra, and cubes.