The Collaborative International Dictionary of English v.0.48:

Chalcocite \Chal"co*cite\, n. [Gr. chalko`s brass.] (Min.)
   Native copper sulphide, called also copper glance, and
   vitreous copper; a mineral of a black color and metallic
   luster. [Formerly written chalcosine.]
   [1913 Webster] Chalcographer

WordNet (r) 3.0 (2006):

chalcocite
    n 1: a heavy grey mineral that is an ore of copper [syn:
         chalcocite, copper glance]