Treatment of iron(III) solutions with alkali leads to
precipitation of the red-brown hydrated iron(III) oxide which when ignited above 200°
leaves the red-brown oxide a-Fe2O3. This oxide occurs naturally as haematite ; it finds uses
in red pigments (ochre, Venetian red) and as a polishing agent in rouge. It has a melting
point of 1565°, density of 5.24 and heat of formation of - 196.5 kcal mole-1.
