The Collaborative International Dictionary of English v.0.48:

Tetrahedrite \Tet`ra*he"drite\, n. [So called because the
   crystals of the species are commonly tetrahedrons.] (Min.)
   A sulphide of antimony and copper, with small quantities of
   other metals. It is a very common ore of copper, and some
   varieties yield a considerable presentage of silver. Called
   also gray copper ore, fahlore, and panabase.
   [1913 Webster]