uraninite n 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 Usage(s) With many such "ifs" Professor Lane estimates the present age of uraninite as 1,070,000,000 years, of pitchblende as 1,300,000,000 years. Synonym(s) pitchblende