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Acanthite

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Formula:
Ag
 
2
S
System:MonoclinicColour:lead grey, black
Lustre:MetallicHardness: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:Aguilarite


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:2.4.1.1
Dana 8th edition ID:2.4.1.1

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

Lustre: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 (measured):7.2 - 7.4 g/cm3
Density (calculated):7.24 g/cm3

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.
Crystal Atlas:
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Argentite no.11 - Goldschmidt (1913-1926)
Argentite - {100}, modified

About Crystal Atlas

The 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.

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Transparency
Opaque | Translucent | Transparent

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X-Ray Powder Diffraction:
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%


Graph shows reflectance levels at different wavelengths (in nm). Peak reflectance is 33.1%.

Chemical Properties of Acanthite

Formula:
Ag
 
2
S
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
Common Impurities:Se

Relationship of Acanthite to other Species

Common Associates:
StephaniteSphaleriteSilverQuartzPyrargyrite
ProustitePolybasiteGalenaChalcopyriteCalcite
Aguilarite
Related Minerals - Nickel-Strunz Grouping):

- +
2.BA.05Chalcocite
Cu
 
2
S
2.BA.05Djurleite
Cu
 
31
S
 
16
2.BA.05Geerite
Cu
 
8
S
 
5
2.BA.05Roxbyite
Cu
 
9
S
 
5
2.BA.10Anilite
Cu
 
7
S
 
4
2.BA.10Digenite
Cu
 
9
S
 
5
2.BA.15Bornite
Cu
 
5
FeS
 
4
2.BA.20Bellidoite
Cu
 
2
Se
2.BA.20Berzelianite
Cu
 
2
Se
2.BA.25Athabascaite
Cu
 
5
Se
 
4
2.BA.25Umangite
Cu
 
3
Se
 
2
2.BA.30Rickardite
Cu
 
7
Te
 
5
2.BA.30Weissite
Cu
 
2-x
Te
2.BA.40Mckinstryite
Ag
 
5-x
Cu
 
3+x
S
 
4
2.BA.40Stromeyerite
AgCuS
2.BA.40dUM2003-13-S:AgAuCu
Ag
 
6
AuCu
 
2
S
 
5
2.BA.45Jalpaite
Ag
 
3
CuS
 
2
2.BA.45Selenojalpaite
Ag
 
3
CuSe
 
2
2.BA.50Eucairite
AgCuSe
2.BA.55Aguilarite
Ag
 
4
SeS
2.BA.55Naumannite
Ag
 
2
Se
2.BA.60Cervelleite
Ag
 
4
TeS
2.BA.60Hessite
Ag
 
2
Te
2.BA.60Chenguodaite
Ag
 
9
Fe
3+
 
Te
 
2
S
 
4
2.BA.65Henryite
Ag
 
3
Cu
 
4
Te
 
4
2.BA.65Stützite
Ag
 
5-x
Te
 
3
, x = 0.24-0.36
2.BA.70Argyrodite
Ag
 
8
GeS
 
6
2.BA.70Canfieldite
Ag
 
8
SnS
 
6
2.BA.70Putzite
(Cu
 
4.7
Ag
 
3.3
)GeS
 
6
2.BA.75Fischesserite
Ag
 
3
AuSe
 
2
2.BA.75Penzhinite
(Ag,Cu)
 
4
Au(S,Se)
 
4
2.BA.75Petrovskaite
AuAg(S,Se)
2.BA.75Petzite
Ag
 
3
AuTe
 
2
2.BA.75Uytenbogaardtite
Ag
 
3
AuS
 
2
2.BA.80Bezsmertnovite
(Au,Ag)
 
4
Cu(Te,Pb)
2.BA.80Bilibinskite
PbCu
 
2
Au
 
3
Te
 
2
2.BA.80Bogdanovite
(Au,Te,Pb)
 
3
(Cu,Fe)
Related Minerals - Hey's Index Grouping:

- +
3.2.3Naumannite
Ag
 
2
Se
3.2.4Aguilarite
Ag
 
4
SeS
3.2.5Hessite
Ag
 
2
Te
3.2.6Empressite
AgTe
3.2.7Stützite
Ag
 
5-x
Te
 
3
, x = 0.24-0.36
3.2.8Cervelleite
Ag
 
4
TeS
3.2.9Dervillite
Ag
 
2
AsS
 
2
3.2.10Stromeyerite
AgCuS
3.2.11Mckinstryite
Ag
 
5-x
Cu
 
3+x
S
 
4
3.2.12Jalpaite
Ag
 
3
CuS
 
2
3.2.13Eucairite
AgCuSe
3.2.14Cameronite
AgCu
 
7
Te
 
10
3.2.15Henryite
Ag
 
3
Cu
 
4
Te
 
4
3.2.16Sternbergite
AgFe
 
2
S
 
3
3.2.17Argentopyrite
AgFe
 
2
S
 
3
3.2.18Geffroyite
(Cu,Fe,Ag)
 
9
(Se,S)
 
8
3.2.19Argentopentlandite
Ag(Fe,Ni)
 
8
S
 
8

Other Names for Acanthite

Synonyms:
AcantiteAkanthiteα-ArgentiteArgentiteArgentite-beta
Argentite-βArgyriteArgyroseBeta-Argentiteβ-Argentite
DaleminziteHenkelitePara-SilberglanzSilver GlanceVitreous Silver
Weicherz
Other Languages:
Catalan:Argentita
Croatian:Argentit
Dutch:Argentiet
French:Acanthite
German:Argentit
Acanthit
Akanthit
α-Argentit
Argyrit
β-Argentit
Glanzerz
Glaserz
Henkelit
Silberglanz
Silberschwärze
Hungarian:Argentit
Italian:Argentite
Japanese:輝銀鉱
Latvian:Argentīts
Lithuanian:Argentitas
Low Saxon:Argentit
Norwegian (Bokmål):Akantitt
Polish:Argentyt
Russian:Аргентит
Simplified Chinese:螺状硫银矿
螺硫银矿
辉银矿
Slovak:Argentit
Spanish:Argentita
Acanthita
Akanthita
α-Argentita
Argyrita
β-Argentita
Henkelita
Swedish:Silverglans
Traditional Chinese:螺狀硫銀礦
Ukrainian:Аргентит
Varieties:
Zincian Acanthite

Other Information

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 LinksSearch for toxicity information at the United States National Library of Medicine

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.

Mindat.org articles about Acanthite

Article entries:
Acanthite from MěděnecRobert Vaňo

Best Localities for Acanthite

Best of Species:Acanthite

Internet Links for Acanthite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Acanthite details from Handbook of Mineralogy (PDF)
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  • 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.
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