The Collaborative International Dictionary of English v.0.48:

Pitchblende \Pitch"blende`\, n. [1st pitch + blende.] (Min.)
   A pitch-black mineral consisting chiefly of the oxide of
   uranium; uraninite. See Uraninite.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pitchblende
    n 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 [syn: uraninite, pitchblende]