massicot, one of the two forms of lead oxide (PbO) that occurs as a mineral (the other form is litharge). Massicot forms by the oxidation of galena and other lead minerals as soft, yellow, earthy or scaly masses that are very dense. It has been found in significant quantities at Badenweiler, Ger.; La Croix-aux-Mines, Fr.; the Transvaal, S.Af.; Perote, Mex.; and Leadville, Colo., U.S. For detailed physical properties, see oxide mineral (table).