cerussite, colorless to white or gray mineral, sometimes yellowish or greenish, transparent to opaque, very brittle, crystallizing in the orthorhombic system and occurring also in granular and massive form. It is a carbonate of lead, PbCO₃, formed by the action of carbonate and bicarbonate solutions on galena. It is an important ore of lead widely distributed throughout the world and found associated with galena and other lead minerals.