Vanadium(III) oxide is the inorganic compound with the formula V2O3. It is a black solid prepared by reduction of V2O5 with hydrogen or carbon monoxide.It is a basic oxide dissolving in acids to give solutions of vanadium(III) complexes. V2O3 has the corundum structure. It is antiferromagnetic with a critical temperature of 160 K. At this temperature there is an abrupt change in conductivity from metallic to insulating.
Upon exposure to air it gradually converts into indigo-blue V2O4.
In nature it occurs as the very rare mineral karelianite.