Answer: uraninite

AnswerCrossword Clue
uraninitemineral, probably originally uranium dioxide, UO2, but altered by radioactive decay, and usually containing uranium trioxide, lead, radium, and helium, occurring in several varieties, including pitchblende: the most important ore of uranium
uraniniteuranium dioxide, the major ore of uranium, found most frequently in botryoidal form as pitchblende