Stephanite

Stephanite is a silver antimony sulfosalt mineral with formula: Ag₅SbS₄ It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal.[4]

Stephanite
General
Category	Sulfosalt mineral
Formula (repeating unit)	Ag5SbS4
Strunz classification	2.GB.10
Dana classification	03.02.04.01
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Cmc21
Identification
Colour	Lead grey to black
Crystal habit	Tabular, pseudo-hexagonal crystals; massive
Twinning	Common on [110] repeated, forms pseudohexagonal groupings
Cleavage	Imperfect on {010}, poor on {021}
Fracture	Subconchoidal
Tenacity	Brittle
Mohs scale hardness	2.0 - 2.5
Lustre	Metallic
Streak	Iron black
Diaphaneity	Opaque
Specific gravity	6.26
Optical properties	Anisotropic in polished section
Pleochroism	Very weak - white to pale pink
References	[1][2][3]

History

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 (Sprödglanzerz), etc. The name stephanite was proposed by W Haidinger in 1845 in honour of the Archduke of Austria Stephan Franz Victor of Habsburg-Lorena (1817-1867). French authors use F. S. Beudant's name psaturose (from the Greek ψαθυρός, fragile).[4]

Properties

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.[4] Stephanite is an important ore of silver in some mining camps.

Occurrence

Stephanite occurs as a late-stage mineral with other ores of silver in hydrothermal veins.[4] Associated minerals include proustite, acanthite, native silver, tetrahedrite, galena, sphalerite and pyrite.[1] Localities which have yielded good crystallized specimens are Freiberg and Gersdorf near Rosswein in Saxony, Chañarcillo in Chile, and exceptionally Cornwall. In the Comstock lode in Nevada massive stephanite and argentite are important ores of silver.

See also

• List of minerals
• List of minerals named after people

References

1. http://rruff.geo.arizona.edu/doclib/hom/stephanite.pdf Handbook of Mineralogy
2. http://webmineral.com/data/Stephanite.shtml Webmineral data
3. http://www.mindat.org/min-3764.html Mindat.org
4. Spencer 1911, p. 880.

Attribution

•  This article incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Stephanite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. 15 (11th ed.). Cambridge University Press. p. 880.