pitchblende (pĭchˈblĕndˌ) [key], dark, lustrous, heavy mineral, a source of radium and uranium. Largely natural uranium oxides, triuranium octaoxide (U3O8) and uranium dioxide (UO2), it usually contains some lead and variable amounts of thorium and rare-earth elements. It is massive in form, frequently with a botryoidal, or grape-cluster, appearance, and has a variable but high specific gravity. Pitchblende is greenish, brownish, or black in color, with a pitchy to submetallic luster. The uranium yield is from 50% to 80%. Uraninite, a closely related ore richer in uranium (uranium dioxide), commonly crystallizes in the cubic system. It yields 65% to 80% uranium and has a specific gravity somewhat higher than that of pitchblende. The color range is from deep black to brown. Both ores occur as primary constituents of quartz veins and with other metals. They supply radium and polonium in addition to uranium. Although the ores occur in small quantities throughout the world, the Great Lakes region of Canada, Congo (Kinshasa), the Czech Republic, the Colorado Plateau, Australia, and South Africa are the major sources.