English: Sylvanite-kaolinite from the Judith Mountains of Montana, USA. (SDSMT 4464, South Dakota School of Mines and Technology, Museum of Geology, Rapid City, South Dakota, USA)

Dark silvery gray = sylvanite White = kaolinite (Al2Si2O5(OH4) - aluminum hydroxy-silicate)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 4900 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The telluride minerals contain one or more telluride anions (Te-2). The tellurides are usually considered together with the sulfide minerals, the arsenide minerals, and the sulfarsenide minerals.

Sylvanite is a rare precious metal telluride mineral, (Au,Ag)2Te4 - gold silver telluride. This mineral volatilizes at relatively low temperatures. With heating, the tellurium component of sylvanite readily vaporizes, leaving behind blebs of gold/silver.

Sylvanite has a metallic luster, a bright silver color, is fairly soft, and usually occurs in the form of elongated blades or small granular masses. It is known from only a few scattered localities on Earth and occurs with other telluride minerals such as calaverite (AuTe2 - gold telluride). Sylvanite is an important gold/silver ore mineral in precious metal telluride deposits such as the Golden Quadrilateral in Romania, near Kalgoorlie in western Australia, and the Cripple Creek Diatreme in Colorado, USA.

---

Photo gallery of sylvanite:

www.mindat.org/gallery.php?min=3849