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Acanthite

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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 άκανθα ("akantha") meaning "thorn", in allusion to its crystal shape.
Dimorph of:
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.


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Classification of AcanthiteHide

Approved, 'Grandfathered' (first described prior to 1959)
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

Pronounciation of AcanthiteHide

Pronounciation:
PlayRecorded byCountry
Jolyon & Katya 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

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 AcanthiteHide

Formula:
Ag2S
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 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 AcanthiteHide

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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Transparency
Opaque | Translucent | Transparent

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X-Ray Powder DiffractionHide

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

Type Occurrence of AcanthiteHide

Synonyms of AcanthiteHide

Other Language Names for AcanthiteHide

Varieties of AcanthiteHide

Relationship of Acanthite to other SpeciesHide

Member of:
Other Members of this group:
AguilariteAg4SeSMon. 2/m
CervelleiteAg4TeSMon. 2/m

Common AssociatesHide

AguilariteAg4SeS
CalciteCaCO3
ChalcopyriteCuFeS2
GalenaPbS
Polybasite[(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]
ProustiteAg3AsS3
PyrargyriteAg3SbS3
QuartzSiO2
SilverAg
SphaleriteZnS
StephaniteAg5SbS4
Associated Minerals Based on Photo Data:
Silver682 photos of Acanthite associated with Silver on mindat.org.
Calcite185 photos of Acanthite associated with Calcite on mindat.org.
Quartz103 photos of Acanthite associated with Quartz on mindat.org.
Polybasite47 photos of Acanthite associated with Polybasite on mindat.org.
Pyrite39 photos of Acanthite associated with Pyrite on mindat.org.
Chalcopyrite39 photos of Acanthite associated with Chalcopyrite on mindat.org.
Proustite38 photos of Acanthite associated with Proustite on mindat.org.
Sphalerite21 photos of Acanthite associated with Sphalerite on mindat.org.
Baryte21 photos of Acanthite associated with Baryte on mindat.org.
Pyrargyrite19 photos of Acanthite associated with Pyrargyrite on mindat.org.

Related Minerals - Nickel-Strunz GroupingHide

2.BA.05ChalcociteCu2SMon. 2/m : P21/b
2.BA.05DjurleiteCu31S16Mon. 2/m
2.BA.05GeeriteCu8S5Trig. 3
2.BA.05RoxbyiteCu9S5Tric. 1 : P1
2.BA.10AniliteCu7S4Orth. mmm (2/m 2/m 2/m) : Pnma
2.BA.10DigeniteCu9S5Trig. 3m (3 2/m) : R3m
2.BA.15BorniteCu5FeS4Orth. mmm (2/m 2/m 2/m) : Pbca
2.BA.20BellidoiteCu2SeTet. 4/m : P42/n
2.BA.20BerzelianiteCu2SeIso. m3m (4/m 3 2/m) : Fm3m
2.BA.25AthabascaiteCu5Se4Orth.
2.BA.25UmangiteCu3Se2Tet.
2.BA.30RickarditeCu7Te5Orth.
2.BA.30WeissiteCu2-xTeHex.
2.BA.40MckinstryiteAg5-xCu3+xS4Orth. mmm (2/m 2/m 2/m) : Pnma
2.BA.40StromeyeriteAgCuSOrth. mmm (2/m 2/m 2/m)
2.BA.40dUM2003-13-S:AgAuCuAg6AuCu2S5
2.BA.45JalpaiteAg3CuS2Tet.
2.BA.45SelenojalpaiteAg3CuSe2Tet. 4/mmm (4/m 2/m 2/m) : I41/amd
2.BA.50EucairiteAgCuSeOrth.
2.BA.55AguilariteAg4SeSMon. 2/m
2.BA.55NaumanniteAg2SeOrth. 2 2 2 : P21 21 21
2.BA.60CervelleiteAg4TeSMon. 2/m
2.BA.60HessiteAg2TeMon. 2/m : P21/b
2.BA.60ChenguodaiteAg9Fe3+Te2S4Orth.
2.BA.65Henryite(Cu,Ag)3+xTe2 , with x ~ 0.40 Iso. m3m (4/m 3 2/m) : Fd3c
2.BA.65StütziteAg5-xTe3, x = 0.24-0.36Hex.
2.BA.70ArgyroditeAg8GeS6Orth. mm2 : Pna21
2.BA.70CanfielditeAg8SnS6Orth. mm2
2.BA.70Putzite(Cu4.7Ag3.3)GeS6Iso. 4 3m : F4 3m
2.BA.75FischesseriteAg3AuSe2Iso. 4 3 2 : I41 3 2
2.BA.75Penzhinite(Ag,Cu)4Au(S,Se)4Hex.
2.BA.75PetrovskaiteAuAg(S,Se)Mon.
2.BA.75PetziteAg3AuTe2Iso. 4 3 2 : I41 3 2
2.BA.75UytenbogaardtiteAg3AuS2Trig. 3m (3 2/m) : R3c
2.BA.80Bezsmertnovite(Au,Ag)4Cu(Te,Pb)Orth.
2.BA.80BilibinskitePbCu2Au3Te2Iso.
2.BA.80Bogdanovite(Au,Te,Pb)3(Cu,Fe)Iso.

Related Minerals - Dana Grouping (8th Ed.)Hide

2.4.1.2NaumanniteAg2SeOrth. 2 2 2 : P21 21 21
2.4.1.3AguilariteAg4SeSMon. 2/m

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

3.2.3NaumanniteAg2SeOrth. 2 2 2 : P21 21 21
3.2.4AguilariteAg4SeSMon. 2/m
3.2.5HessiteAg2TeMon. 2/m : P21/b
3.2.6EmpressiteAgTeOrth. mmm (2/m 2/m 2/m)
3.2.7StütziteAg5-xTe3, x = 0.24-0.36Hex.
3.2.8CervelleiteAg4TeSMon. 2/m
3.2.9DervilliteAg2AsS2Mon. 2/m : P2/b
3.2.10StromeyeriteAgCuSOrth. mmm (2/m 2/m 2/m)
3.2.11MckinstryiteAg5-xCu3+xS4Orth. mmm (2/m 2/m 2/m) : Pnma
3.2.12JalpaiteAg3CuS2Tet.
3.2.13EucairiteAgCuSeOrth.
3.2.14CameroniteCu5-x(Cu,Ag)3+xTe10 (x = 0.43)Mon. 2/m : B2/b
3.2.15Henryite(Cu,Ag)3+xTe2 , with x ~ 0.40 Iso. m3m (4/m 3 2/m) : Fd3c
3.2.16SternbergiteAgFe2S3Orth. mmm (2/m 2/m 2/m)
3.2.17ArgentopyriteAgFe2S3Mon. 2/m
3.2.18Geffroyite(Cu,Fe,Ag)9(Se,S)8Iso. m3m (4/m 3 2/m) : Fm3m
3.2.19ArgentopentlanditeAg(Fe,Ni)8S8Iso. m3m (4/m 3 2/m) : Fm3m

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

Common component of (items highlighted in red)

References for AcanthiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften (1855) IV, 447-468.
Kenngott, A. (1855) Ueber den Akanthit, eine neue Species in dem Geschlechte der Silber-Glanze. Annalen der Physik und Chemie: 95: 462-464.
Palache, C., Berman, H., Frondel, C. (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.
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) X-ray study on the alpha-beta transition of Ag2S Locality: Innai mine, Akita, Japan. Mineralogical Journal (Japan): 5: 124-148.
Petruk, W., Owens, D. R., Stewart, J.M., Murray, E.J. (1974) Observations on acanthite, aguilarite and naumannite. The Canadian Mineralogist: 12: 365-369.
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.
Pingitore, N.E,, Ponce, B.F., Estrada, L., Eastman, M.P., Yuan, H.L., Porter, L.C., Estrada, G. (1993) Calorimetric analysis of the system Ag2S-Ag2Se between 25 and 250°C. Journal of Material Research: 8: 3126-3130.
Gaines, Richard V., H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, Abraham Rosenzweig, Vandall King (1997) Dana's New Mineralogy: The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, 8th. edition, p. 42.

Internet Links for AcanthiteHide

Localities for AcanthiteHide

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