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Acanthite

A valid IMA mineral species - grandfathered
This page kindly sponsored by Mark Kucera
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About AcanthiteHide

Formula:
Ag2S
Colour:
lead grey, black
Lustre:
Metallic
Hardness:
2 - 2½
Specific Gravity:
7.2 - 7.4
Crystal System:
Monoclinic
Member of:
Name:
Named in 1855 by Gustav Adolf Kenngott from the Greek ฮฌฮบฮฑฮฝฮธฮฑ ("akantha") meaning "thorn", in allusion to the thorn-like crystal shape of his material. With the advent of instrumental analytical equipment, it was discovered that the mineral called "argentite" which had isometric crystal shapes has an atomic structure and chemistry identical to acanthite.
Dimorph of:
Isostructural with:
Acanthite is the low-temperature modification of silver sulphide.

All natural silver sulphide specimens at room temperatures are acanthite.
The structure of Argentite, the high-temperature cubic (isometric) form cannot be quenched. At atmospheric pressure, argentite is stable above 177ยฐC and acanthite is stable below 177ยฐC. Most acanthite crystals are paramorphs, which formed above the transition temperature and retain an isometric shape below the transition temperature, but have monoclinic symmetry at the atomic level.

The tarnish on manufactured sterling silver objects is chemically the same as acanthite.


Unique IdentifiersHide

Mindat ID:
10
Long-form identifier:
mindat:1:1:10:5

Similar NamesHide

IMA Classification of AcanthiteHide

Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Ag1+2S2-

Classification of AcanthiteHide

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

Mineral SymbolsHide

As of 2021 there are now IMAโ€“CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.

SymbolSourceReference for Standard
AcaIMAโ€“CNMNCWarr, L.N. (2021). IMAโ€“CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43

Pronunciation of AcanthiteHide

Pronunciation:
PlayRecorded byCountry
Jolyon RalphUnited Kingdom

Physical Properties of AcanthiteHide

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

Optical Data of AcanthiteHide

Anisotropism:
Weak
Reflectivity:
WavelengthR1 (%)
400nm32.8%
420nm32.9%
440nm33.0%
460nm33.1%
480nm33.0%
500nm32.7%
520nm32.0%
540nm31.2%
560nm30.5%
580nm29.9%
600nm29.2%
620nm28.7%
640nm28.2%
660nm27.6%
680nm27.0%
700nm26.4%


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

Chemistry of AcanthiteHide

Mindat Formula:
Ag2S
Element Weights:
Element% weight
Ag87.060 %
S12.940 %

Calculated from ideal end-member formula.
Ag
S
CAS Registry number:
21548-73-2

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

Crystallography of AcanthiteHide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
Cell Parameters:
a = 4.229 Å, b = 6.931 Å, c = 7.862 Å
β = 99.61°
Ratio:
a:b:c = 0.61 : 1 : 1.134
Unit Cell V:
227.21 ร…ยณ (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. Large primary crystals are uncommon, other than fine overgrowths and replacements of native silver; they are prismatic to long prismatic, elongated along [001], to 2.5 cm, may be tubular; also massive.

Crystallographic forms of AcanthiteHide

Crystal Atlas:
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Argentite no.11 - {111} - Goldschmidt (1913-1926)
View 3D crystal model
Argentite - {100}, modified
3d models and HTML5 code kindly provided by www.smorf.nl.

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IDSpeciesReferenceLinkYearLocalityPressure (GPa)Temp (K)
0010584AcanthiteFrueh A J (1958) The crystallography of silver sulfide, Ag2S Zeitschrift fur Kristallographie 110 136-1441958Freiberg, Saxony, Germany0293
CIF Raw Data - click here to close

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
3.96 ร…(10)
3.571 ร…(6)
3.437 ร…(35)
3.383 ร…(20)
3.080 ร…(60)
2.836 ร…(70)
2.664 ร…(45)
2.606 ร…(100)
2.583 ร…(70)
2.456 ร…(70)
2.440 ร…(80)
2.421 ร…(60)
2.383 ร…(80)
2.213 ร…(45)
2.093 ร…(16)
2.083 ร…(45)
2.072 ร…(16)
2.047 ร…(16)
1.995 ร…(16)
1.963 ร…(20)
1.935 ร…(4)
1.918 ร…(4)
1.903 ร…(14)
1.866 ร…(16)
1.816 ร…(4)
1.798 ร…(4)
1.733 ร…(12)
1.718 ร…(20)
1.691 ร…(6)
1.610 ร…(4)
1.587 ร…(14)
1.579 ร…(10)
1.554 ร…(8)
1.540 ร…(8)
1.513 ร…(12)
1.483 ร…(10)
1.470 ร…(10)
1.459 ร…(14)
1.379 ร…(6)
Comments:
ICDD 14-72

Geological EnvironmentHide

Paragenetic Mode(s):
Paragenetic ModeEarliest Age (Ga)
High-๐‘‡ alteration and/or metamorphism
33 : Minerals deposited by hydrothermal metal-rich fluids (see also [#12])
Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere<0.6
49 : Oxic cellular biomineralization (see also #44)<0.54
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 Jรกchymov (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 Chaรฑarcillo, south of Copiapรณ, Atacama, Chile.

Type Occurrence of AcanthiteHide

Synonyms of AcanthiteHide

Other Language Names for AcanthiteHide

Varieties of AcanthiteHide

Zinc-bearing AcanthiteClearly needs reliable verification.

Relationship of Acanthite to other SpeciesHide

Member of:
Other Members of Acanthite Group:
AguilariteAg4SeSMon. 2/m : P21/c
CervelleiteAg4TeSMon. 2/m : P21/c

Common AssociatesHide

Associations Based on Photo Data:
1,397 photos of Acanthite associated with Native SilverAg
436 photos of Acanthite associated with CalciteCaCO3
384 photos of Acanthite associated with QuartzSiO2
200 photos of Acanthite associated with PyriteFeS2
180 photos of Acanthite associated with Polybasite[Ag6Sb2S7][Ag9CuS4]
168 photos of Acanthite associated with ChalcopyriteCuFeS2
149 photos of Acanthite associated with GalenaPbS
149 photos of Acanthite associated with PyrargyriteAg3SbS3
123 photos of Acanthite associated with SphaleriteZnS
119 photos of Acanthite associated with ProustiteAg3AsS3

Related Minerals - Strunz-mindat GroupingHide

2.BA.MakotoiteAg12(Cu3Au)S8Trig. 3m(32/m) : R3c
2.BA.AlburniteAg8GeTe2S4Iso.
2.BA.DzierลผanowskiteCaCu2S2Trig. 3m(32/m) : P3m1
2.BA.XuwenyuaniteAg9Fe3+Te2S4Iso. 43m : F43m
2.BA.'Orileyite'(Fe,Cu)2As
2.BA.JuxingiteBi6Cu+138Cu2+2Fe3+30S125Iso. 43m : F43m
2.BA.LuoxianchangiteAg8SnS4Se2Orth. mmm(2/m2/m2/m)
2.BA.05DjurleiteCu31S16Mon. 2/m : P21/c
2.BA.05GeeriteCu8S5Trig. 3
2.BA.05RoxbyiteCu58S32Tric. 1 : P1
2.BA.05ChalcociteCu2SMon. 2/m : P21/c
2.BA.10DigeniteCu9S5Trig. 3m(32/m) : R3m
2.BA.10AniliteCu7S4Orth. mmm(2/m2/m2/m) : Pnma
2.BA.15BorniteCu5FeS4Orth. mmm(2/m2/m2/m) : Pbca
2.BA.20BellidoiteCu2SeTet. 4/m : P42/n
2.BA.20BerzelianiteCu2-xSe (x โ‰ˆ 0.12)Iso. m3m(4/m32/m) : Fm3m
2.BA.25AthabascaiteCu5Se4Orth.
2.BA.25UmangiteCu3Se2Tet. 42m : P421m
2.BA.30RickarditeCu7Te5Orth. mmm(2/m2/m2/m) : Pmmn
2.BA.30WeissiteCu2-xTeHex. 6/mmm(6/m2/m2/m) : P6/mmm
2.BA.35SpryiteAg8(As3+0.5As5+0.5)S6Orth. mm2 : Pna21
2.BA.40d'UM2003-13-S:AgAuCu'Ag6AuCu2S5
2.BA.40MckinstryiteAg5-xCu3+xS4Orth. mmm(2/m2/m2/m) : Pnma
2.BA.40StromeyeriteAgCuSOrth. mmm(2/m2/m2/m)
2.BA.42HoneaiteAu3TlTe2 Orth. mmm(2/m2/m2/m) : Pbcm
2.BA.45JalpaiteAg3CuS2Tet. 4/mmm(4/m2/m2/m) : I41/amd
2.BA.45SelenojalpaiteAg3CuSe2Tet. 4/mmm(4/m2/m2/m) : I41/amd
2.BA.45KuriliteAg8Te3SeTrig. 3 : R3
2.BA.47Spiridonovite(Cu1-xAgx)2TeTrig. 3m(32/m) : P3c1
2.BA.50WuyanzhiiteCu2STet. 422 : P43212
2.BA.50EucairiteAgCuSeOrth.
2.BA.52'Argentite'Ag2SIso.
2.BA.55NaumanniteAg2SeOrth. 222 : P212121
2.BA.55AguilariteAg4SeSMon. 2/m : P21/c
2.BA.60ChenguodaiteAg9Fe3+Te2S4Orth.
2.BA.60HessiteAg2TeMon. 2/m : P21/c
2.BA.60CervelleiteAg4TeSMon. 2/m : P21/c
2.BA.65Henryite(Cu,Ag)3+xTe2 , with x ~ 0.40Iso. m3m(4/m32/m) : Fd3c
2.BA.65StรผtziteAg5-xTe3, x = 0.24-0.36Hex. 6 : P6
2.BA.70ArgyroditeAg8GeS6Orth. mm2 : Pna21
2.BA.70Putzite(Cu4.7Ag3.3)GeS6Iso. 43m : F43m
2.BA.70CanfielditeAg8SnS6Orth. mm2 : Pna21
2.BA.75FischesseriteAg3AuSe2Iso. 432 : I4132
2.BA.75UytenbogaardtiteAg3AuS2Trig. 3m(32/m) : R3c
2.BA.75Penzhinite(Ag,Cu)4Au(S,Se)4Hex. 622 : P6322
2.BA.75PetrovskaiteAuAgSMon.
2.BA.75PetziteAg3AuTe2Iso. 432 : I4132
2.BA.80Bezsmertnovite(Au,Ag)4Cu(Te,Pb)Orth.
2.BA.80BilibinskitePbCu2Au3Te2Iso.
2.BA.80Bogdanovite(Au,Te,Pb)3(Cu,Fe)Iso.

Fluorescence of AcanthiteHide

Not fluorescent in UV

Other InformationHide

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

Acanthite in petrologyHide

An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.

    Internet Links for AcanthiteHide

    References for AcanthiteHide

    Reference List:

    Localities for AcanthiteHide

    Showing 3,905 localities.

    This 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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