Stephanite

Stephanite

Stephanite single crystal perched on calcite (size: 0.7 mm)
General
Category Sulfosalt mineral
Formula
(repeating unit)		 Ag5SbS4
Strunz classification 2.GB.10
Dana classification 03.02.04.01
Crystal system Orthorhombic
Identification
Colour Lead grey to black
Crystal habit Tabular, pseudo-hexagonal crystals; massive
Crystal symmetry Orthorhombic - pyramidal
H-M symbol (mm2)
Space group: C mc21
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]

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]

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

References

  1. 1 2 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. 1 2 3 4 Spencer 1911, p. 880.
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