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Acanthite

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Fresnillo de Gonzalez Echeverria (Fresnillo), Mun. de Fresnillo, Zacatecas, Mexico
© Brent Thorne

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Formula:
Ag
 
2
S
System:MonoclinicColour:lead grey, black
Lustre:MetallicHardness:2 - 2½
Name:Dana 7th, and The Handbook of Mineralogy, say it is from the greek "akantha" meaning thorn, alluding to 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 in. At atmospheric pressure, argentite is stable above 177°C and acanthite is stable below 177°C. The tarnish on Sterling silver is 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), Ostrov, Krušné Hory Mts (Erzgebirge), Karlovy Vary Region, Bohemia (Böhmen; Boehmen), Czech Republic
Year of Discovery:1855

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 (P1 1 21/m) [P21/m] {P1 21/m 1}
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.
Crystal Atlas:
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Argentite no.11 - Goldschmidt (1913-1926)
Argentite - {100}, modified

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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)

Chemical Properties of Acanthite

Formula:
Ag
 
2
S
Essential elements:Ag, S
All elements listed in formula:Ag, S
Common Impurities:Se

Relationship of Acanthite to other Species

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.35Argentite
2.BA.40Mckinstryite
(Ag,Cu)
 
2
S
2.BA.40Stromeyerite
AgCuS
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.65Henryite
Ag
 
3
Cu
 
4
Te
 
4
2.BA.65Stützite
Ag
 
7
Te
 
4
2.BA.70Argyrodite
Ag
 
8
GeS
 
6
2.BA.70Canfieldite
Ag
 
8
(Sn,Ge)(S,Te)
 
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
PbCuAu
 
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
 
7
Te
 
4
3.2.8Cervelleite
Ag
 
4
TeS
3.2.9Dervillite
Ag
 
2
AsS
 
2
3.2.10Stromeyerite
AgCuS
3.2.11Mckinstryite
(Ag,Cu)
 
2
S
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:
α-ArgentiteAcantiteAkanthiteArgentiteArgentite-β
Argentite-betaArgyriteArgyroseβ-ArgentiteBeta-Argentite
DaleminziteHenkelitePara-SilberglanzSilver GlanceVitreous Silver
Weicherz
German names:
α-ArgentitAcanthitAkanthitArgentitArgyrit
β-ArgentitGlanzerzHenkelitSilberglanz
Russian names:
Аргентит
Spanish names:
α-ArgentitaAcanthitaAkanthitaArgentitaArgyrita
β-ArgentitaHenkelita
Swedish names:
Silverglans
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.

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.

Sitzungsber. Kaiserl. Akad. (1855), IV, 447-468.

Dana's New Mineralogy, 8th Edition, Gaines et.al., p. 42.

Internet Links for Acanthite

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  • Raman and XRD data at RRUFF project
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  • Acanthite details from Handbook of Mineralogy (PDF)
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    Localities for Acanthite

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