Overview
Calaverite is a gold telluride mineral and one of the most important natural sources of gold beyond native metal. Brass-yellow to silvery-white with a bright metallic lustre, it can easily be mistaken for pyrite or even native gold, yet it is chemically very different: the gold here is locked up with tellurium rather than occurring as the free element. Named in 1868 after Calaveras County, California, calaverite played a notable role in the great gold-telluride bonanzas of the late nineteenth and early twentieth centuries.
Composition & structure
Calaverite is gold ditelluride, AuTe2, in which gold is combined with tellurium rather than with oxygen or sulfur. It crystallises in the monoclinic system, typically as bladed or short prismatic crystals that are often striated, and it lacks cleavage. A small amount of the gold can be substituted by silver. Calaverite is famous in crystallography for its complex, "incommensurate" crystal structure, whose puzzling crystal faces resisted conventional indexing for many years and were only fully explained with modern structural techniques.
| Formula | AuTe2 |
| Crystal system | Monoclinic |
| Mohs hardness | 2.5 to 3 |
| Lustre | Metallic |
| Colour | Brass-yellow to silver-white |
| Type locality | Calaveras County, California, USA |
Formation & occurrence
Calaverite forms in hydrothermal gold deposits, particularly in low-temperature epithermal veins associated with volcanic terrains where tellurium is available. It is deposited from hot, circulating fluids alongside other tellurides, native gold, pyrite and quartz. Such tellurium-rich gold systems are geologically special, and where they occur calaverite can be a major ore mineral. On weathering, calaverite breaks down and the tellurium is lost, often leaving behind spongy or "mustard" native gold — a transformation that historically alerted miners to the richness of telluride ores.
Identification & similar species
The metallic brass-yellow colour and high density are immediate clues, but calaverite is easily confused with pyrite, native gold and other gold tellurides such as sylvanite and krennerite. Unlike soft, malleable native gold, calaverite is brittle. Distinguishing it from sylvanite and krennerite, which share similar appearances and chemistries, usually requires careful study; sylvanite contains essential silver, while krennerite is closely related to calaverite in composition. Because the gold is bound to tellurium, calaverite does not behave like free gold in simple tests, which historically caused some telluride ores to be overlooked.
Notable localities & collecting
The type locality is Calaveras County, California, but the most spectacular specimens came from Cripple Creek, Colorado, where rich gold-telluride veins yielded superb crystallised calaverite, including a famously vug discovered in the Cresson mine in 1914 lined with gold tellurides and native gold. Outstanding material has also come from Kalgoorlie in Western Australia, another world-class telluride goldfield, as well as from Romania and other epithermal districts. Because of its gold content and historical importance, crystallised calaverite is highly desirable, and fine sharp crystals from the classic camps are genuine museum-grade rarities.