Pitchblende

Pitchblende, or uraninite, brown, black, or greenish radioactive mineral, the most important source of uranium, radium, and polonium. The composition varies between UO₂ and UO_2.6; thorium, radium, polonium, lead, and helium are also present. Principal deposits are in Zaire and Czechoslovakia, at Great Bear Lake in Canada, and in the U.S. Mountain States.