Stephanite

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Stephanite is a silver antimony sulfide mineral with formula: Ag₅SbS₄ It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal.

Under the name Schwarzerz it was mentioned by Georgius Agricola in 1546, and it has been variously known as "black silver ore" (German Schwarzgultigerz), brittle silver-ore (Sprodglanzerz), etc. The name stephanite was proposed by W Haidinger in 1845 in honour of the archduke Stephan of Austria; French authors use F. S. Beudant's name psalurose (from the Greek ψαλoυρος, fragile).

It frequently occurs as well-formed crystals, which are orthorhombic and occasionally show indications of hemimorphism: they have the form of six-sided prisms or flat tables terminated by large basal planes and often modified at the edges by numerous pyramid-planes. Twinning on the prism-planes is of frequent occurrence, giving rise to pseudo-hexagonal groups like those of aragonite. The colour is iron-black, and the lustre metallic and brilliant; on exposure to light, however, the crystals soon become dull.

The mineral has a Mohs hardness of 2-2.5 and is very brittle; the specific gravity is 6.3. Stephanite occurs with other ores of silver in metalliferous veins. Localities which have yielded good crystallized specimens are Freiberg and Gersdorf near Rosswein in Saxony, Chanarcillo in Chile, and exceptionally Cornwall. In the Comstock lode in Nevada massive stephanite and argentite are important ores of silver.

[edit] References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.