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Acanthite

This page kindly sponsored by david mustart
Formula:
Ag2S
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.
Isostructural with:
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

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
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 ed.:
2.4.1.1
2.4.1.1

2 : SULFIDES
4 : AmBnXp, with (m+n):p = 2:1
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

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

Metallic
Diaphaneity (Transparency):
Opaque
Colour:
lead grey, black
Streak:
lead grey
Hardness (Mohs):
2 - 2½
Hardness (Vickers):
VHN50=21 - 25 kg/mm2
Hardness Data:
Measured
Tenacity:
Sectile
Cleavage:
None Observed
Fracture:
Sub-Conchoidal
Density:
7.2 - 7.4 g/cm3 (Measured)    7.24 g/cm3 (Calculated)

Crystallography of Acanthite

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
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 ų (Calculated from Unit Cell)
Z:
4
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 [001], to 2.5 cm, may be tubular; massive.

Crystallographic forms of Acanthite

Crystal Atlas:
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Argentite no.11 - Goldschmidt (1913-1926)
Argentite - {100}, modified
3d models and HTML5 code kindly provided by www.smorf.nl.

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Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

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Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation
X-Ray Powder Diffraction Data:
d-spacingIntensity
3.08(60)
2.84(70)
2.61(100)
2.58(70)
2.46(70)
2.44(80)
2.42(60)
2.38(80)

Optical Data of Acanthite

Type:
Anisotropic
Anisotropism:
Weak
Reflectivity:
400nmR=32.8%
420nmR=32.9%
440nmR=33.0%
460nmR=33.1%
480nmR=33.0%
500nmR=32.7%
520nmR=32.0%
540nmR=31.2%
560nmR=30.5%
580nmR=29.9%
600nmR=29.2%
620nmR=28.7%
640nmR=28.2%
660nmR=27.6%
680nmR=27.0%
700nmR=26.4%

Reflectance graph
Graph shows reflectance levels at different wavelengths (in nm). Top of box is 100%. Peak reflectance is 33.1%.

Chemical Properties of Acanthite

Formula:
Ag2S
Essential elements:
All elements listed in formula:
CAS Registry number:
21548-73-2

CAS Registry numbers are published by the American Chemical Society
Common Impurities:
Se

Relationship of Acanthite to other Species

2.BA.05ChalcociteCu2S
2.BA.05DjurleiteCu31S16
2.BA.05GeeriteCu8S5
2.BA.05RoxbyiteCu9S5
2.BA.10AniliteCu7S4
2.BA.10DigeniteCu9S5
2.BA.15BorniteCu5FeS4
2.BA.20BellidoiteCu2Se
2.BA.20BerzelianiteCu2Se
2.BA.25AthabascaiteCu5Se4
2.BA.25UmangiteCu3Se2
2.BA.30RickarditeCu7Te5
2.BA.30WeissiteCu2-xTe
2.BA.40MckinstryiteAg5-xCu3+xS4
2.BA.40StromeyeriteAgCuS
2.BA.40dUM2003-13-S:AgAuCuAg6AuCu2S5
2.BA.45JalpaiteAg3CuS2
2.BA.45SelenojalpaiteAg3CuSe2
2.BA.50EucairiteAgCuSe
2.BA.55AguilariteAg4SeS
2.BA.55NaumanniteAg2Se
2.BA.60CervelleiteAg4TeS
2.BA.60HessiteAg2Te
2.BA.60ChenguodaiteAg9Fe3+Te2S4
2.BA.65Henryite(Cu,Ag)3+xTe2 , with x ~ 0.40
2.BA.65StütziteAg5-xTe3, x = 0.24-0.36
2.BA.70ArgyroditeAg8GeS6
2.BA.70CanfielditeAg8SnS6
2.BA.70Putzite(Cu4.7Ag3.3)GeS6
2.BA.75FischesseriteAg3AuSe2
2.BA.75Penzhinite(Ag,Cu)4Au(S,Se)4
2.BA.75PetrovskaiteAuAg(S,Se)
2.BA.75PetziteAg3AuTe2
2.BA.75UytenbogaardtiteAg3AuS2
2.BA.80Bezsmertnovite(Au,Ag)4Cu(Te,Pb)
2.BA.80BilibinskitePbCu2Au3Te2
2.BA.80Bogdanovite(Au,Te,Pb)3(Cu,Fe)
3.2.3NaumanniteAg2Se
3.2.4AguilariteAg4SeS
3.2.5HessiteAg2Te
3.2.6EmpressiteAgTe
3.2.7StütziteAg5-xTe3, x = 0.24-0.36
3.2.8CervelleiteAg4TeS
3.2.9DervilliteAg2AsS2
3.2.10StromeyeriteAgCuS
3.2.11MckinstryiteAg5-xCu3+xS4
3.2.12JalpaiteAg3CuS2
3.2.13EucairiteAgCuSe
3.2.14CameroniteCu5-x(Cu,Ag)3+xTe10 (x = 0.43)
3.2.15Henryite(Cu,Ag)3+xTe2 , with x ~ 0.40
3.2.16SternbergiteAgFe2S3
3.2.17ArgentopyriteAgFe2S3
3.2.18Geffroyite(Cu,Fe,Ag)9(Se,S)8
3.2.19ArgentopentlanditeAg(Fe,Ni)8S8

Other Names for Acanthite

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Acanthite

Reference List:
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.

Internet Links for Acanthite

Specimens:
The following Acanthite specimens are currently listed for sale on minfind.com.

Localities for Acanthite

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.
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