Acanthite is a form of silver sulfide with the chemical formula Ag₂S. It crystallizes in the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

system and is the stable form of silver sulfide below .

Argentite In mineralogy, argentite (from the Latin ''argentum'', silver) is cubic silver sulfide (Ag2S), which can only exist at temperatures above 173 °C, 177 °C or 179 °C. When it cools to ordinary temperatures it turns into its mono ...

is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C acanthite forms directly. Acanthite is the only stable form in normal air temperature.

Occurrence

Acanthite is a common silver mineral in moderately low-temperature

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

veins and in zones of supergene enrichment. It occurs in association with native silver,

pyrargyrite Pyrargyrite is a sulfosalt mineral consisting of silver sulfantimonite, Ag3SbS3. Known also as dark red silver ore or ruby silver, it is an important source of the metal. It is closely allied to, and isomorphous with, the corresponding sulfarse ...

, proustite, polybasite,

stephanite Stephanite is a silver antimony sulfosalt mineral with formula: Ag5 Sb S4. It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal. History Under the name Schwarzerz it was mentioned by Georgius Agricola in 1546, an ...

, aguilarite, galena,

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mo ...

, sphalerite, calcite and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

. Acanthite was first described in 1855 for an occurrence in the Jáchymov (St Joachimsthal) District, Krušné Hory Mts ( Erzgebirge), Karlovy Vary Region, Bohemia,

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

. The name is from the Greek "akantha" meaning thorn or arrow, in reference to its crystal shape.

Gallery

File:Acanthite - Chispas Mine, Arizpe, Sonora, Mexico.jpg, Acanthite - Locality: Chispas Mine,

Arizpe Arizpe (or Arispe) is a small town and the municipal seat of the Arizpe Municipality in the north of the Mexican state of Sonora. It is located at 30°20'"N 110°09'"W. The area of the municipality is 2,806.78 sq.km. The population in 2005 was ...

, Sonora, Mexico. Scale is one inch with a ruled line at one cm. File:Acanthite-180757.jpg, Classic acanthite specimen from the Rayas Mine at Guanajuato, Mexico.Size: 2.4 x 1.1 x 1.1 cm.

References

{{ores Sulfide minerals Silver minerals Monoclinic minerals Minerals in space group 14