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|System:||Monoclinic||Colour:||lead grey, black|
|Lustre:||Metallic||Hardness:||2 - 2½|
|Name:||Named in 1855 by Gustav Adolf Kenngott from the Greek άκανθα ("akantha") meaning "thorn", in allusion to its crystal shape.|
Acanthite is the low-temperature modification of silver sulphide.
All natural silver sulphide specimens at room temperature are acanthite.
The structure of Argentite, the high-temperature cubic (isometric) form cannot be quenched. At atmospheric pressure, pure argentite is stable above 177°C and acanthite is stable below 177°C. The tarnish on sterling silver is chemically the same as acanthite.
Classification of Acanthite
|IMA status:||Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"|
|Strunz 8th edition ID:||2/B.05-10|
|Strunz 9th edition ID:||2.BA.35|
|Nickel-Strunz 10th (pending) edition ID:||2.BA.35|
2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
B : Metal Sulfides, M: S > 1: 1 (mainly 2: 1)
A : With Cu, Ag, Au
|Dana 7th edition ID:||220.127.116.11|
|Dana 8th edition ID:||18.104.22.168|
2 : SULFIDES
4 : AmBnXp, with (m+n):p = 2:1
|Hey's CIM Ref.:||3.2.1|
3 : Sulphides, Selenides, Tellurides, Arsenides and Bismuthides (except the arsenides, antimonides and bismuthides of Cu, Ag and Au, which are included in Section 1)
2 : Sulphides etc. of Ag
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Type Occurrence of Acanthite
|Type Locality:||Jáchymov (St Joachimsthal), Jáchymov District (St Joachimsthal), Krušné Hory Mts (Erzgebirge), Karlovy Vary Region, Bohemia (Böhmen; Boehmen), Czech Republic|
|Year of Discovery:||1855|
Occurrences of Acanthite
|Geological Setting:||A common silver species in moderately low-temperature hydrothermal sulphide veins, and in zones of secondary enrichment. |
Widespread in silver deposits. Localities for fine primary and paramorphic crystals include: Jáchymov (St Joachimsthal), Czech Republic [TL]; In Germany, at Freiberg, Schneeberg, Annaberg, and Marienberg, Saxony; and from St Andreasberg, Harz. 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 Chañarcillo, south of Copiapó, Atacama, Chile.
Physical Properties of Acanthite
|Colour:||lead grey, black|
|Hardness (Mohs):||2 - 2½|
|Hardness (Vickers):||VHN50=21 - 25 kg/mm2|
|Density (measured):||7.2 - 7.4 g/cm3|
|Density (calculated):||7.24 g/cm3|
Crystallography of Acanthite
|Class (H-M):||2/m - Prismatic|
|Cell Parameters:||a = 4.229Å, b = 6.931Å, c = 7.862Å|
β = 99.61°
|Ratio:||a:b:c = 0.61 : 1 : 1.134|
|Unit Cell Volume:||V 227.21 Å³ (Calculated from Unit Cell)|
|Morphology:||Typically found as pseudo-cubic and pseudo-octahedral crystals, paramorphic after argentite. Also found as thorn-shaped monoclinic crystals, usually small to microscopic in size. Primary crystals are rare, prismatic to long prismatic, elongated along , to 2.5 cm, may be tubular; massive.|
About Crystal AtlasThe mindat.org Crystal Atlas allows you to view a selection of crystal drawings of real and idealised crystal forms for this mineral and, in certain cases, 3d rotating crystal objects. The 3d models and HTML5 code are kindly provided by www.smorf.nl.
Edge Lines | Miller Indicies | Axes
Opaque | Translucent | Transparent
Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation
|X-Ray Powder Diffraction:|
Optical Data of Acanthite
Graph shows reflectance levels at different wavelengths (in nm). Peak reflectance is 33.1%.
Chemical Properties of Acanthite
|Simplified for copy/paste:||Ag2S|
|Essential elements:||Ag, S|
|All elements listed in formula:||Ag, S|
|CAS Registry number:||21548-73-2|
CAS Registry numbers are published by the American Chemical Society
Relationship of Acanthite to other Species
|Related Minerals - Nickel-Strunz Grouping):|
|Related Minerals - Hey's Index Grouping:|
Other Names for Acanthite
|Health Warning:||No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.|
|External Links||Search for toxicity information at the United States National Library of Medicine|
References for Acanthite
Palache, Charles, Harry Berman & Clifford Frondel (1944) The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged, 834pp.: 191-192.
Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften (1855) IV, 447-468.
Frueh, A. J. (1957) The crystal structure, polymorphism and twinning of acanthite (Ag2S). Acta Crystallographica, 10, 764-764.
Frueh, A. J. (1958) The crystallography of silver sulfide, Ag2S. Zeitschrift für Kristallographie, 110, 136-144.
Sadanaga, R. & Sueno, S. (1967) Mineral. J. (Japan), 5, 124.
Petruk, W.; Owens, D. R.; Stewart, J. M.; Murray, E. J. (1974) Observations on acanthite, aguilarite and naumannite. Canadian Mineralogist, 12, 365-369.
Dana's New Mineralogy, 8th Edition, Gaines et.al., p. 42.
Cava, R. J., Reidinger, F. & Wuensch, B. J. (1980) Single-crystal neutron diffraction study of the fast-ion conductor β-Ag2S between 186 and 325°C. Journal of Solid State Chemistry, 31, 69-80.
Mindat.org articles about Acanthite
Best Localities for Acanthite
|Best of Species:||Acanthite|
Internet Links for Acanthite
|Specimens:||The following Acanthite specimens are currently listed for sale on minfind.com.|
Localities for Acanthite
The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.