High Quality Content by WIKIPEDIA articles! Thorianite is a rare mineral, originally discovered by Ananda Coomaraswamy in 1904 as uraninite, but recognized as a new species by Wyndham R. Dunstan. It was so named on account of its high percentage of thorium (about 70% ThO2); it also contains the oxides of uranium, lanthanum, cerium and didymium (praseodymium and neodymium). Helium is present, and the mineral is slightly less radioactive than pitchblende but harder to shield due its high energy gamma rays. It is more common in the alluvial gem-gravels of Sri Lanka, where it occurs mostly as water worn, small, heavy, black, cubic crystals. The largest crystals (sizes usually up to around 1.5 cm; very rare are sizes greater than 2.5 cm; largest is 6 cm and 2.2 kilos) came from Madagascar.