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Download hereGENERAL DESCRIPTION
Acanthite is a silver sulphide. It is the most important silver ore, after silver-bearing galena. This species is common in metalliferous hydrothermal veins of low-to medium temperature.
It comes from the transformation of argentite (high temperature form, unstable below 173°C). The cubic or pseudo-octahedral crystals of argentite end up being transformed into acanthite, while preserving their form.
The real crystals of acanthite are rare. In a general way, acanthite is black with a metallic lustre. The largest cubes of acanthite after argentite measure up to 8 cm. This silver sulphide is often associated to native silver, pyrargyrite, proustite or with galena.
The Jachimov, Freiberg and Annaberg deposits in Germany/Czech Republic or the Mexican mines of Guanajuata are famous for Acanthite. Recently, amazing set of crystals were found in Imiter, Morocco and in various Chinese mines.
Acanthite is also present in many localities in France: the Rhun mine in Plélauff (Côtes d'Armor), the Sylvestre mine in Alsace, the Ste-Lucie mine in Lozère. There are also many other localities in Haute-Loire.
The type of this species is preserved in the "collection of the Emperor" at the Naturhistorische Museum in Vienna, Austria.
HISTORY : Name inspired from the Greek word "ακαντα" [akanta] meaning "arrow", in reference to its crystal shapes
Species first described in 1855 by Gustav Adolf Kenngott (1818-1897), Swiss mineralogist
Type-locality: Jachimov, République Tchèque
CHEMICAL FORMULA : Ag2S
CRYSTAL SYSTEM : Monoclinic
COLOR : Black, grayish
DIAPHANIETY : Opaque
LUSTER : Metallic
STREAK : Lead gray
MORPHOLOGIE : Crystals sometimes prismatic, more often cubo-octahedric
HARDNESS : 2,0-2,5
CHEMICAL CLASS: 7,24
DENSITY : II - Sulfides, arsenides, antimonides and selenides
GROUP : Acanthite
STRUNZ CLASS BEFORE 2001 : 2/B.05-10
STRUNZ CLASS AFTER 2001 : 2.BA.25
