Dims: 1.61x1.11x0.41in (4.09x2.81x1.04cm) .... Wt: 0.53oz (14.9g) .... Loc: Cripple Creek Mining District, Teller County, Colorado, USA
All of the silvery specs on this specimen are calaverite, the rare gold telluride mineral. A loupe reveals that the calaverite is arrayed in lines, knees, and other jagged shapes that remind one of letters written in some cryptic language - a classic feature of this mineral. The calaverite is draped over a druze of purple fluorite and white quartz. Very rare, very nice. It would be perfect if a loupe wasn't needed to truly appreciate it!
Calaverite is an uncommon and much sought after mineral by mineral collectors and those seeking fortunes.
Calaverite is one of the few minerals that is an ore of gold, besides native gold itself.
It is the most common gold bearing mineral besides native gold.
The element gold is typically either found as native gold (in its elemental state), as
an alloy with other metals such as silver and copper and as trace amounts in a few minerals.
To be an actual significant part of a non-alloyed mineral is really quite uncommon for gold and this makes calaverite a unique mineral indeed.
For some reason gold has an affinity for the element tellurium, which is sometimes found naturally as
Tellurium is a semi-metallic element which means that it has some properties of metals but not all or as strongly.
This helps provide an explanation for gold's, and other metals such as silver's, attraction to tellurium.
Other gold tellurides include sylvanite, (Silver Gold Telluride);
kostovite, (Copper Gold Telluride);
krennerite, (Silver Gold Telluride);
nagyagite, (Gold Lead Antimony Iron Telluride Sulfide) and
petzite(Silver Gold Telluride).
Calaverite is closely related to
sylvanite and differs only in silver content and slightly in hardness, cleavage, color and density.
At times the two minerals are only distinguishable with chemical tests.
Crystals of calaverite are unique and of interest to collectors.
Typically found as striated prisms that can be twinned causing sharp bends, reticulated individuals and skeletal or arborescent formations.
These clusters remind many collectors of writing.
Color is silver white to brassy yellow.
Luster is a bright metallic.
Transparency: Crystals are opaque.
Crystal System: Monoclinic; 2/m
Crystal Habits include prismatic to more rarely tabular crystals that are often twinned into sharp
bends, reticulated individuals and skeletal or arborescent formations.
These are sometimes described as looking like writing.
Also found as granular masses.
Cleavage is absent.
Fracture is conchoidal.
Hardness is 2.5 - 3
Specific Gravity is approximately 9.1 - 9.3 (very heavy even for metallic minerals).
Streak is a yellow gray.
Other Characteristics: Crystals tend to be deeply striated parallel to the prominent length.
Notable Occurrences include Cripple Creek in Teller County, Colorado and Calaveras County (from where it gets its name),
California, USA; Nagyag, Romania; Kirkland lake Gold District, Ontario and
Rouyn District, Quebec, Canada and Kalgoorlie, Australia.
Best Field Indicators are crystal habit, density, softness, color, luster, association with other tellurides and gold and lack of cleavage.