Home Minerals Acanthite


Acanthite is a form of silver sulfide with the chemical formula: Ag2S. It crystallizes inside the monoclinic gadget and is the solid form of silver sulfide under 173 °C (343 °F). A silver sulfide, it is the maximum important ore of silver. It additionally happens in huge form and has an opaque, grayish black color. Above 350°F (177°C), silver sulfide crystallizes in the cubic machine, and it was assumed that cubic silver sulfide, known as argentite changed into a separate mineral from acanthite. it’s miles now known that they may be the identical mineral, with acanthite crystallizing within the monoclinic system at temperatures beneath 350°F (177°C). Acanthite forms in hydrothermal veins with other minerals, which includes silver, galene, pyrargyrite, and proustite. It also paperwork as a secondary alteration made from number one silver sulfides. when heated, acanthite fuses quite simply and releases sulfurous fumes. The maximum famous locality of acanthite, the Comstock Lode in Nevada, united states of america, turned into so wealthy in silver that a department of the usa mint was established at close by Carson city to coin its output.

Name: From the Greek for thorn, in allusion to the shape of the crystals.

Association: Silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite, galena, chalcopyrite, sphalerite, calcite, quartz.

Polymorphism & Series: The high-temperature cubic form (“argentite”) inverts to acanthite at about 173 ◦C; below this temperature acanthite is the stable phase and forms directly

Crystallography: Isometric; hexoctahedral. Crystals most commonly show the cube, octahedron, and dodecahedron, but are frequently distorted and arranged in branching or reticulated groups. Most commonly massive, or as a coating.

Acanthite Composition: Silver sulfide, Ag2S. Ag = 87.1 per cent, S = 12.9 per cent.

Diagnostic Features: Argentite can be distinguished by its color, sectility, and high specific gravity.

Environment: In hydrothermal deposits and epithermal veins.

Chemical Properties

Chemical Classification Sulfide mineral
Formula Ag2S
Common Impurities Se

Acanthite Physical Properties

Crystal habit Primary crystals rare, prismatic to long prismatic, elongated along [001], may be tubular; massive. Commonly paramorphic after the cubic high-temperature phase (“argentite”), of original cubic or octahedral habit
Color Lead grey, black
Streak lead grey
Luster Metallic
Cleavage None Observed
Diaphaneity Opaque
Mohs Hardness 2 – 2,5
Crystal System Monoclinic
Tenacity Sectile
Density 7.2 – 7.4 g/cm3 (Measured)    7.24 g/cm3 (Calculated)
Fracture Sub-Conchoidal

Acanthite Optical Properties

Type Anisotropic
Anisotropism Weak
Twinning Polysynthetic on {111}, may be very complex due to inversion; contact on {101}

Occurrence of Acanthite

Argentite is an critical primary silver mineral found in veins related to local silver, the ruby silvers, polybasite, stephanite, galena, and sphalerite. it could also be of secondary starting place. it’s miles located in microscopic inclusions in so-called argentiferous galena. Argentite is an important ore in the silver mines of Guanajuato and some place else in Mexico; in Peru, Chile, and Bolivia. vital ecu localities for its prevalence are Freiberg in Saxony, Joachimsthal in Bohemia, Schemnitz and Kremnitz in Czechoslovakia, Kongsberg in Norway. in the united states of america it’s been an important ore mineral in Nevada, appreciably on the Comstock Lode and at Tonopah. it’s also found in the silver districts of Colorado, and in Montana at Butte related to copper ores.

Acanthite Uses Area

  • An important ore of silver
  • This mineral has aesthetic price and is precious because of its shortage.
  • it may be an effective manner of decreasing steel availability and toxicity in infected soils.
  • The sharpening on Sterling silver is Acanthite.   


Widespread in silver deposits.

  • Localities for fine primary and paramorphic crystals include: from J´achymov (Joachimsthal), Czech Republic [TL].
  • In Germany, at Freiberg, Schneeberg, Annaberg, and Marienberg, Saxony; and from St. Andreasberg, Harz Mountains.
  • In Mexico, large paramorphs from Arizpe, Sonora; in the Rayas and other mines at Guanajuato; and from many mines in Zacatecas, Chihuahua, etc.
  • In the USA, at Butte, Silver Bow Co., Montana; Tonopah, Nye Co., and the Comstock Lode, Virginia City, Storey Co., Nevada.
  • From various mines at Cobalt, Ontario, Canada.
  • At Chanarcillo, south of Copiapo, Atacama, Chile.


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• Dana, J. D. (1864). Manual of Mineralogy… Wiley.
• Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
• Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
• Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].