Zinc Chromite, ZnO.Cr₂O₃

Zinc Chromite, ZnO.Cr₂O₃, is obtained by heating chromium trioxide and zinc oxide with boric acid, or by heating potassium chromate in hydrogen or carbon dioxide containing zinc chloride vapour.

Zinc chromite thus prepared consists of microscopic regular octa- hedra with a very dark green colour. They are harder than quartz, and their density at 15° C. is 5.29, or 5.309 at 11° C.

Acids do not attack it, potassium bisulphate only with great difficulty, but it is decomposed by fused potassium hydroxide and nitrate.

An insoluble violet zinc chromite, 8ZnO.3Cr₂O₃, has been obtained by fusing zinc potassium chromate.

A dark brownish-violet powder of zinc thiochromite, ZnO.Cr₂S₃, was prepared by heating zinc oxide with sulphur in a stream of hydrogen and then in sulphur vapour. It decomposes into greyish-green zinc chromite when heated in air.