Acanthite is a form of

silver sulfide Silver sulfide is an inorganic compound with the formula . A dense black solid, it is the only sulfide of silver. It is useful as a photosensitizer in photography. It constitutes the tarnish that forms over time on silverware and other silver ob ...

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 Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

system and is the stable form of silver sulfide below .

Argentite In mineralogy, argentite () is cubic silver sulfide (Ag2S), which can only exist at temperatures above , , or . When it cools to ordinary temperatures it turns into its monoclinic polymorph, acanthite. The International Mineralogical Associatio ...

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 Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...

and in zones of supergene enrichment. It occurs in association with native silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite,

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...

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 Mohs scale, hardness of 3.5 to 4 ...

sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

. Acanthite was first described in 1855 for an occurrence in the

Jáchymov Jáchymov (; or ''Joachimsthal'') is a spa town in Karlovy Vary District in the Karlovy Vary Region of the Czech Republic. It has about 2,300 inhabitants. Jáchymov has a long mining tradition, thanks to which it used to be the second most popu ...

(Joachimsthal) district,

Ore Mountains The Ore Mountains (, or ; ) lie along the Czech–German border, separating the historical regions of Bohemia in the Czech Republic and Saxony in Germany. The highest peaks are the Klínovec in the Czech Republic (German: ''Keilberg'') at ab ...

Bohemia Bohemia ( ; ; ) is the westernmost and largest historical region of the Czech Republic. In a narrow, geographic sense, it roughly encompasses the territories of present-day Czechia that fall within the Elbe River's drainage basin, but historic ...

(today

Karlovy Vary Region The Karlovy Vary Region () is an administrative unit () of the Czech Republic, located in the westernmost part of the country. It is named after its capital Karlovy Vary. It is known for spas, which include Karlovy Vary and Mariánské Lázně. ...

, Czech Republic). 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,

Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...

, 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 Guanajuato, officially the Free and Sovereign State of Guanajuato, is one of the 32 states that make up the Political divisions of Mexico, Federal Entities of Mexico. It is divided into Municipalities of Guanajuato, 46 municipalities and its cap ...

, Mexico. Size: 2.4 × 1.1 × 1.1 cm.

References

{{Ores Sulfide minerals Silver minerals Monoclinic minerals Glances Minerals in space group 14 Minerals described in 1855

Occurrence

Gallery

See also

References