The Collaborative International Dictionary of English v.0.48:

Sylvanite \Syl"van*ite\, n. [Fr. Transylvania, where first
   found.] (Min.)
   A telluride of gold and silver, (Au, Ag)Te2, of a steel
   gray, silver white, or brass yellow. It often occurs in
   implanted crystals resembling written characters, and hence
   is called graphic tellurium. H., 1.5-2. Sp.gr., 7.9-8.3.
   [Webster 1913 Suppl.]