Of
the minerals containing gold the most important are sylvanite or
graphic tellurium, of composition (AgAu) Te, with 24,, to 26 per cent;
cala-verite, AuTe2, with 42 per cent; and nagyagite or
foliate tellurium, of a complex and rather indefinite composition, with
5 to 9 per cent of gold. These are confined to a few localities, the
oldest and best known being those of Nagyag and Ofenbanya, in
Transylvania; but latterly they have been found in some quantity at Red
Cloud, Colorado, and in Calaveras county, California— the nearly pure
telluride of gold, calaverite, biing confined to these places.
The
minerals of the second class, usually spoken of as auriferous, or
containing gold in sensible quantity, though not to a sufficient
amount to form an essential in the chemical formulas, or even in many
instances to be found in the quantities ordinarily operated upon in
analyses, are comparatively numerous, including many of the metallic
sulphides. Prominent among these are galena and iron pyrites,—the
former, according to the observations of Percy and Smith, being almost
invariably goldbearing to an extent that can be recognized in
operating upon a pound weight of the lead smelted from it. the
