Thorianite is a rare thorium , ThO2. It was originally described by Ananda Coomaraswamy but recognized as a new species by Wyndham R. Dunstan It was so named on account of its high percentage of thorium; it also contains the oxides of uranium , praseodymium is present, and the mineral is slightly less radioactive than pitchblende, but is harder to shield due to its high energy gamma rays. It is common in the alluvial , where it occurs mostly as water worn, small, heavy, black, cubic crystals. The largest crystals are usually near 1.5 cm. Larger crystals, up to 6 cm (2.4 in), have been reported from Madagascar.