1. A complex brownish-black mineral, UO2, forming the chief ore of uranium and containing variable amounts of radium, lead, thorium, and other elements. it is isomorphous with thorianite.

1. any of several brownish-black forms of uranium dioxide, UO2, (especially pitchblende) that is the chief ore of uranium; it is isomorphous with thorianite.

1. A mineral consisting chiefly of uranium oxide with some lead, thorium, etc., occurring in black octahedrons, also in masses with a pitchlike luster; pitchblende.

1. this mineral, in its different varieties (the crystallized kinds called cleveite, bröggerite, nivenite, etc., and the more abundant amorphous and impure pitchblende), has become of much importance as being the chief source of radium. see radium and radioactivity. from the investigation of it also has been derived a large part of our present knowledge of the transformation of uranium into radium and the further successive changes of the latter element with lead as the probable final step: all analyses have shown a small amount of this element whose presence was hitherto unexplained. it has also been found that many varieties of uraninite yield the gas helium, which is one of the early transformation products of radium.
2. A mineral of a pitch-black color and very heavy, having when unaltered a specific gravity of 9.5.

1. a mineral consisting of uranium oxide and trace amounts of radium and thorium and polonium and lead and helium; uraninite in massive form is called pitchblende which is the chief uranium ore