thorianite

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A highly radioactive blackish, greenish, or yellow mineral, ThO₂, isomorphous with uraninite.

Century Dictionary and Cyclopedia

1. n. A mineral found in alluvial gravel near Kondurugala, in the province of Sabaragamuwa, and in the Galle district, Ceylon. It occurs in small roughly cubical crystals, of brownish-black color and resinous luster, of specific gravity 9.5–9.7, of hardness nearly 7, infusible before the blowpipe, easily pulverized, and then readily soluble in strong nitric acid. The mineral is strongly radioactive and consists essentially of the oxids of thorium, uranium, the rare earths, and lead. Two varieties have been described, the one containing 78 per cent, of thorium dioxid and 12 per cent. of uranium oxid, the other containing about 60 per cent. of thorium dioxid and over 30 per cent, of uranium oxid. Both varieties contain a relatively high proportion of helium, the former on solution setting free something over ten cubic centimeters of this rare gas. The mineral can properly be classed as a variety of uraninite or pitchblende.

Wiktionary

1. n. mineralogy A radioactive mineral containing thorium dioxide (ThO2) plus oxides of uranium, lanthanum, cerium neodymium and praseodymium in smaller quantities.