iron(III) oxide

A red-brown to black insoluble solid, Fe₂O₃; trigonal; r.d. 5.24; m.p. 1565°C. There is also a hydrated form, Fe₂O₃.xH₂O, which is a red-brown powder; r.d. 2.44–3.60. (See rusting.)

Iron(III) oxide occurs naturally as haematite and can be prepared by heating iron(III) hydroxide or iron(II) sulphate. It is readily reduced on heating in a stream of carbon monoxide or hydrogen.