Sylvanite

Webster's Dictionary of the English Language

·noun A mineral, a telluride of gold and silver, of a steel-gray, silver-white, or brass-yellow color. It often occurs in implanted crystals resembling written characters, and hence is called graphic tellurium.

II. Sylvanite ·add. ·noun 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.