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Sylvanite Coating on Quartz
SULFIDES; TELLURIDES · MONOCLINIC

Sylvanite

(Au,Ag)Te4

Hardness
1.5–2
Streak
Dark gray to black
Spec. Gravity
7.9–8.3
System
Monoclinic

About

Sylvanite is a unique mineral that forms with both gold and silver in its structure. Sylvanite is structurally similar to Calaverite, but it contains silver in its structure in addition to gold. If less than 13.4% of silver is replaced by gold, it is no longer classified as Sylvanite, but rather Calaverite. 
The name Sylvanite is derived from sylvanium, which was an original name proposed for the element tellurium. Tellurium is present within Sylvanite, and its first documented occurrence was in the Transylvania region of Romania - hence the name sylvanium.

Crystal Forms & Aggregates

Striking Features

Color, crystal habits, and mode of occurrence

Environment

Uses

Sylvanite is an ore of gold and silver. It is also rare collector's mineral, with special value due to its gold content.

Noteworthy Localities

Veins and dendritic growths of Sylvanite , some with patterns, come from the Transylvania in Romania at Baia de Arieş (Offenbánya), Alba Co.; and Sacarîmb (Nagyág), Hunedoara Co. Elongated crystals often with deep striations or skeletal/hoppered growths are highly regarded from the Emperor Mine, Vatukoula, Viti Levu, Fiji. 
There are several important Colorado localities of Sylvanite; most notable is the Cripple Creek District, Teller Co., Colorado. Other Colorado localities include the Keystone Mine, Magnolia District, Boulder Co.; the Jamestown District, Boulder Co., and the Bessie G Mine, La Plata Co., Colorado.

Common Mineral Associations

Distinguishing Similar Minerals

Photos

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Crystal forms

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Prismatic
Tabular