CALAVERITE & SYLVANITE
Calaverite and sylvanite are rare precious metal telluride
minerals. Calaverite is gold telluride (AuTe2) and sylvanite
is gold silver telluride ((Au,Ag)2Te4). The
telluride minerals volatilize at relatively low temperatures. With heating,
the tellurium component of these minerals readily vaporizes, leaving behind
blebs of gold or gold/silver.
Calaverite has a metallic luster, a yellowish-gold to
silvery color, is moderately soft, and has a variety of crystal forms.
Sylvanite has a metallic luster, a bright silver color, is fairly soft, and
usually occurs in the form of elongated blades or small granular masses.
Calaverite & sylvanite occur with other telluride
minerals, and are known from only a few scattered localities on Earth.
They are important gold & gold/silver ore minerals in precious metal
telluride deposits such as the Golden Quadrilateral in Romania, near Kalgoorlie
in western Australia, and the Cripple Creek Diatreme in Colorado, USA.
Calaverite (gold) (field of view ~1.7 cm across) in a purple fluorite vein, from
the Cripple Creek Diatreme (Early Oligocene, 32 million years) of central
Colorado, USA.
Sylvanite (bright silver) (field of view 1.2 cm across) from Boulder County,
Colorado, USA.