Calaverite

Calaverite is a gold telluride (AuTe2) and one of the most important telluride ores of gold. It is brass-yellow to silvery-white, soft, and metallic, crystallizing in the monoclinic system as bladed or striated crystals, though it often occurs in massive or granular form.

Named after Calaveras County, California, calaverite is significant because much of the gold in some major deposits is locked in tellurides rather than as native metal, a fact that historically fooled miners who discarded the unremarkable-looking ore.

Unlike native gold, calaverite tarnishes and is brittle, and it requires special processing to extract the gold it contains.

Calaverite forms in low-temperature hydrothermal gold deposits, particularly epithermal vein systems associated with volcanic rocks, where tellurium is available to combine with gold. It is a primary ore mineral in several world-class gold districts.

It occurs with other tellurides such as sylvanite, krennerite, and petzite, plus native gold, pyrite, quartz, and fluorite. The most famous localities are Cripple Creek, Colorado, and Kalgoorlie, Western Australia, where calaverite-bearing ore yielded immense amounts of gold; other occurrences are in Romania, Canada, and elsewhere.

Look for a brass-yellow to silver-white metallic mineral that is soft (Mohs 2.5-3), brittle, and relatively dense, often as bladed, striated crystals or grains in quartz veins. The streak is yellowish to greenish-gray.

It can be confused with pyrite (harder, more truly brass-yellow, cubic) and with native gold (which is soft but malleable and does not tarnish), as well as other gold-silver tellurides. Calaverite's brittleness (versus malleable gold), tarnish, and telluride association distinguish it; definitive identification often uses chemical or instrumental tests, including heating to release a telluride odor.

Calaverite is mined as a major ore of gold; in districts like Cripple Creek and Kalgoorlie it was the principal gold-bearing mineral, so its recognition was economically crucial. The gold is recovered by roasting or other processing that frees it from the telluride.

Fine crystals are also prized by collectors as classic gold-telluride specimens. It has no gemstone use because it is soft and tarnishes, and no real metaphysical tradition; its importance is economic and mineralogical. The tellurium content means it should be handled sensibly.