Sylvanite
Gold silver telluride ((Au,Ag)Te2)
A silver-white gold-silver telluride and important gold-silver ore, noted for crystals arranged in writing-like graphic patterns.
- Mohs hardness
- 1.5-2
- Color
- Silver-white to steel-gray, metallic
- Type
- mineral
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Overview
Sylvanite is a gold-silver telluride ((Au,Ag)Te2) and an important ore of both metals. It is silver-white to steel-gray with a bright metallic luster and is very soft, crystallizing in the monoclinic system, often as bladed or skeletal crystals.
It is famous for arranging its crystals in branching, rune-like or letter-like patterns, giving rise to the nickname "graphic tellurium." The name derives from Transylvania, the region where tellurium and its minerals were first studied.
Like calaverite, sylvanite hides gold in a telluride that does not look like gold, making its recognition important in telluride gold districts.
Formation & geology
Sylvanite forms in low-temperature epithermal hydrothermal veins associated with gold-silver-telluride mineralization, typically in volcanic-hosted systems where tellurium combines with gold and silver. It is a primary ore mineral in several major districts.
It occurs with calaverite, krennerite, petzite, native gold, native tellurium, pyrite, quartz, and fluorite. Classic localities include Transylvania (Romania), Cripple Creek in Colorado, Kalgoorlie in Western Australia, and other telluride gold camps; the graphic intergrowths are especially associated with the original European occurrences.
How to identify it
Look for a soft (Mohs 1.5-2), silver-white to steel-gray, brittle metallic mineral, often in bladed crystals forming distinctive branching, writing-like (graphic) patterns, with a gray to grayish-black streak.
The graphic habit and pale silver-gray color help distinguish it from the more yellow calaverite and from pyrite (much harder). It resembles other tellurides and some sulfosalts, so confirmation may need chemical testing; like other tellurides it can give off a telluride odor when heated. Its extreme softness and metallic sheen are useful clues.
Uses & significance
Sylvanite is mined as an ore of gold and silver and was an important contributor to production in telluride gold districts such as Cripple Creek, Kalgoorlie, and Transylvania. The precious metals are recovered by roasting or other processing that removes the tellurium.
Well-formed graphic specimens are also valued by collectors as classic telluride minerals. It has no gemstone use because it is extremely soft and tarnishes, and little metaphysical tradition; its significance is primarily economic and mineralogical.
Frequently asked questions
What metals does sylvanite contain?
It is a telluride of both gold and silver ((Au,Ag)Te2) and is mined as an ore of both precious metals.
Why is sylvanite called graphic tellurium?
Because its crystals often grow in branching, letter- or rune-like patterns that resemble writing.
How do you tell sylvanite from calaverite?
Sylvanite is more silver-white to steel-gray and contains silver, while calaverite is more brass-yellow and is essentially a gold-only telluride; sylvanite is also softer.
Where was sylvanite first found?
It is named after Transylvania in Romania, where its tellurium minerals were first studied.
Sylvanite guides
In-depth guides for identifying, valuing, and understanding Sylvanite.
