Argyrodite

Argyrodite is an uncommon silver germanium sulfide mineral with formula Ag₈GeS₆. The color is iron-black with a purplish tinge, and the luster metallic.

Argyrodite
General
Category	Sulfide mineral
Formula (repeating unit)	Ag8GeS6
Strunz classification	2.BA.35
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Pna21
Unit cell	a = 15.149, b = 7.476 c = 10.589 [Å]; Z = 4
Identification
Color	Black, purplish tinge
Crystal habit	Pseudo-octahedra or pseudo-cubic, dodecahedra, cubes; radiating crystal aggregates, botryoidal crusts, or massive
Twinning	Pseudospinel law {111} penetration twins
Cleavage	Absent
Fracture	Uneven to conchoidal
Mohs scale hardness	2.5
Luster	Metallic
Diaphaneity	Opaque
Specific gravity	6.2-6.5
Optical properties	Weakly anisotropic
Pleochroism	Weak
References	[1][2]

Discovered by Clemens Winkler in 1886,[3] it is of interest as it was described shortly after the element germanium was isolated, 15 years after it had been postulated by Mendeleev. It was first described for an occurrence in the Himmelsfürst Mine, Erzgebirge, Freiberg, Saxony, Germany.[2]

The Freiberg mineral had previously been imperfectly described by August Breithaupt under the name "Plusinglanz", and Bolivian crystals were incorrectly described in 1849 as crystallized brongniardite.[3]

Isomorphous with argyrodite is the corresponding tin bearing mineral Ag₈SnS₆, also found in Bolivia as pseudocubic crystals, and known by the name canfieldite.[3] There is also a related mineral, putzite, with composition (Cu_4.7Ag_3.3)GeS₆.

Argyrodite gets its name from the Greek words that loosely translate into "rich in silver".[1]

References

1. Handbook of Mineralogy
2. Mindat.org
3. Spencer 1911, p. 488.

Attribution:

•  This article incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Argyrodite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. 2 (11th ed.). Cambridge University Press. p. 488.