Thorianite

Usually found in alluvial deposits, beach sands, heavy mineral placers, and pegmatites. Sri Lanka – In stream gravels, Galle district, Southern Province; Balangoda district; near Kodrugala, Sabaragamuwa Province; and from a pegmatite in Bambarabotuwa area. India – Reported from beach sands of Travancore (Kerala). Madagascar – Found in alluvial deposits of Betroka and Andolobe. Also as very large crystals from Tôlanaro (Fort Dauphin); at Andranondambo and other localities. Russia – In black sands of a gold placer on Boshogoch River, Transbaikalia, Siberia; in the Kovdor Massif by Kovdor, Kola Peninsula; in the Yenisei Range, Siberia. United States – reported from Easton, Pennsylvania; black sands in Missouri River, near Helena, Montana; Scott River, Siskiyou County, California; black sands in Nixon Fork and Wiseman districts, Alaska. Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca; Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario. South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal. Democratic Republic of Congo - Kasaï region

Based on color, specific gravity and composition three types of thorianite are distinguished: α-thorianite β-thorianite γ-thorianite Thorianite and uraninite form a complete solid solution series in synthetic and natural material. The division between the two species is at Th:U = 1:1 with U possibly making up to 46.50% and Th ranging up to 87.88%. Rare earths, chiefly Ce, substitute for Th in amounts up to 8% by weight. Ce is probably present as Ce. Complete series is known in synthetic material between CeO2 - PrO2 - ThO2 - UO2. Small amounts of Fe and Zr also may be isomorphous with Th. Pb present is probably radiogenic.