Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite. It is a green powder with strong coloring strength and covering strength. Specific gravity: 5.21g /ml. Melting point:2266. Boiling point: 4000. Insoluble in water, sparingly insoluble in acids, comparatively stable in the atmosphere, not react with acid and alkali of average concentration and sulfur dioxide, with excellent pigmental quality and outstanding color fastness.
It is not readily attacked by acids or bases, although molten alkali gives chromites (salts with the Cr 2O24 anion, not to be confused with the related mineral chromite). It turns brown when heated, but reverts to its dark green color when cooled. It is also hygroscopic.
Chromium oxide is amphoteric. Although insoluble in water, it dissolves in acid to produce hydrated chromium ions, [Cr(H2O)6]3+. It dissolves in concentrated alkali to yield chromite ions. Cr2O3 occurs by nature inward mineral eskolaite, which embodies came up in chromium-rich tremolite skarns, metaquartzites, and chlorite veins. Eskolaite is also a rare component of chondrite meteorites. The mineral is named after Suomi geologist Pentti Eskola.
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