Dictionary:

sylvanite

  (sĭl'və-nīt')

A pale brass-yellow to silver-white ore of gold and silver, chiefly (Au,Ag)Te₂.

[French, after TRANSYLVANIA.]

Environment

Rare; in late low-temperature precious metal ore veins.

Usually in crystals, deeply striated, elongated parallel to a horizontal axis. Commonly twinned and difficult to orient; structurally a real challenge. Also granular and massive.

Pale brass yellow to silver-white. Luster metallic; hardness 2Ɖ specific gravity 8.2 (sylvanite) to 9.3 (calaverite); fracture uneven; cleavage none or (sylvanite) a side pinacoid cleavage. Brittle.

Inseparable tellurides of gold and of silver (44.03% Au, 55.97% Te). Calaverite becomes sylvanite when 13.4% of its gold is replaced by silver.

Gives ice blue tint to flames flaring from bead on charcoal, eventually shrinking into a gold button. A higher silver content of sylvanite makes bead whiter.

The deeply striated, elongated, and flat-lying crystals are unmistakable; they are usually the lone metallic glints on specimens. The gold assay bead is easy to obtain and can hardly be misidentified.

Calaverite is a rare mineral, but an important ore of gold in Kalgoorlie, Western Australia; Calaveras Co., California; and Cripple Creek, Colorado. In the veins it is associated only with sylvanite, other tellurides, tellurium, quartz, and fluorite, as a rule with no base metal ores. Cripple Creek was the only really spectacular occurrence of this mineral. Sylvanite is also found with related minerals in Nagyág and Offenbånya in Transylvania. "Blister-gold" specimens, sold long ago in Colorado to tourists as natural gold when Cripple Creek was in production, are actually examples of these two ores that were roasted to drive off the tellurium and bring bubbles of gold to the surface. The structure of these minerals has proved one of the most tantalizing problems that x-ray mineralogists have encountered. Current thinking has classified them as triclinic and twinned.

The noun has one meaning:

Meaning #1: a silver-white mineral consisting of silver gold telluride; a source of gold in Australia and America
  Synonym: graphic tellurium

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