Chromium(III) oxide is a dark green chemical that has a formula of CrO. It is composed of chromium in its +3 oxidation state and oxide ions. It can react with other metal oxides in basic conditions to make chromates. It is made from chromium ore and is part of the process for making chromium metal. It was used as a pigment. It dissolves in acid to produce chromium(III) salts, such as chromium(III) chloride. Stainless steel's corrosion resistance is based on this compound. A thin layer of this compound forms on the surface of the stainless steel. It prevents the rest of the steel from oxidizing.