The Collaborative International Dictionary of English v.0.48:

Leucopyrite \Leu*cop"y*rite\ (l[-u]*k[o^]p"[i^]*r[imac]t), n.
   [Leuco- + pyrites.] (Min.)
   A mineral of a color between white and steel-gray, with a
   metallic luster, and consisting chiefly of arsenic and iron.
   [1913 Webster]