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Polybasite

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Formula:
[(Ag,Cu)
 
6
(Sb,As)
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
System:MonoclinicColour:Black with dark ruby ...
Lustre:MetallicHardness:2½ - 3
Member of:Pearceite Group
Name:From the Greek πολύς, poly, "many" and βάσις, basis, "a base" in allusion to the many base elements present.
Isostructural with:Pearceite


Pearceite Group, Pearceite-Polybasite series.

One of the four "ruby silvers" (pyrargyrite, proustite and miargyrite are the other three).
Two structural varieties (trigonal, P321 and monoclinic, C2/c) are known (Evain et al., 2006).

In a nomenclature change in 2006, the old name antimonpearceite was replaced by polybasite-Tac, arsenpolybasite-221 by pearceite-T2ac, arsenpolybasite-222 by pearceite-M2a2b2c, polybasite-221 by polybasite-T2ac, and polybasite-222 by polybasite-M2a2b2c (Bindi et al., 2007).

Classification of Polybasite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:2/E.05-50
Nickel-Strunz 10th (pending) edition ID:2.GB.15

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
G : Sulfarsenites, sulfantimonites, sulfbismuthites
B : Neso-sulfarsenites, etc. with additional S
Dana 8th edition ID:3.1.7.2

3 : SULFOSALTS
1 : ø > 4
Hey's CIM Ref.:5.2.12

5 : Sulphosalts - Sulpharsenites and Sulphobismuthites (those containing Sn, Ge,or V are in Section 6)
2 : Sulpharsenites etc. of Ag
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Occurrences of Polybasite

Geological Setting:In low to medium temperature hydrothermal veins

Physical Properties of Polybasite

Lustre:Metallic
Diaphaneity (Transparency):Opaque
Colour:Black with dark ruby red internal reflections
Streak: black
Hardness (Mohs):2½ - 3
Tenacity:Very brittle
Cleavage:Imperfect/Fair
Imperfect on {001}
Fracture:Conchoidal
Density (measured):6.1 g/cm3
Density (calculated):6.36 g/cm3

Crystallography of Polybasite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:B2/m {B1 1 2/m} {C2/m} {C1 2/m 1}
Cell Parameters:a = 26.17Å, b = 15.11Å, c = 23.89Å
β = 90°
Ratio:a:b:c = 1.732 : 1 : 1.581
Unit Cell Volume:V 9,446.79 ų (Calculated from Unit Cell)
Z:16
Morphology:Always in pseudo hexagonal trillings, as tablets and rosettes
Twinning:{110}
Crystal Atlas:
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Polybasite no.4 - Goldschmidt (1913-1926)
Polybasite no.5 - Goldschmidt (1913-1926)
Polybasite - Tabular {001}
Polybasite - Tabular {001}

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X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Polybasite

Type:Biaxial (-)
Type:Anisotropic
Anisotropism:Moderate
Colour in reflected light:gray white
Internal Reflections:Red
Pleochroism:Weak
Comments:n>2.72

Chemical Properties of Polybasite

Formula:
[(Ag,Cu)
 
6
(Sb,As)
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
Simplified for copy/paste:[(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]
Essential elements:Ag, Cu, S, Sb
All elements listed in formula:Ag, As, Cu, S, Sb
Common Impurities:As,Fe

Relationship of Polybasite to other Species

Series:Forms a series with Pearceite (see here)
Member of:Pearceite Group
Other Members of Group:

- +
Cupropearceite
[Cu
 
6
As
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
Cupropolybasite
[Cu
 
6
Sb
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
Pearceite
[(Ag,Cu)
 
6
(As,Sb)
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
Selenopolybasite
[(Ag,Cu)
 
6
(Sb,As)
 
2
(S,Se)
 
7
][Ag
 
9
Cu(S,Se)
 
2
Se
 
2
]
Related Minerals - Nickel-Strunz Grouping):

- +
2.GB.05Argentotennantite
Ag
 
6
[Cu
 
4
(Fe,Zn)
 
2
]As
 
4
S
 
13
2.GB.05Freibergite
Ag
 
6
[Cu
 
4
Fe
 
2
]Sb
 
4
S
 
13-x
2.GB.05Giraudite
Cu
 
6
[Cu
 
4
(Fe,Zn)
 
2
]As
 
4
Se
 
13
2.GB.05Goldfieldite
Cu
 
12
(Te,Sb,As)
 
4
S
 
13
2.GB.05Hakite
Cu
 
6
[Cu
 
4
Hg
 
2
]Sb
 
4
Se
 
13
2.GB.05Tennantite
Cu
 
6
[Cu
 
4
(Fe,Zn)
 
2
]As
 
4
S
 
13
2.GB.05Tetrahedrite
Cu
 
6
[Cu
 
4
(Fe,Zn)
 
2
]Sb
 
4
S
 
13
2.GB.10Selenostephanite
Ag
 
5
Sb(Se,S)
 
4
2.GB.10Stephanite
Ag
 
5
SbS
 
4
2.GB.15Pearceite
[(Ag,Cu)
 
6
(As,Sb)
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
2.GB.15UM2003-14-S:AgBiFeTe
Ag
 
16
FeBiTe
 
3
S
 
8
2.GB.15Selenopolybasite
[(Ag,Cu)
 
6
(Sb,As)
 
2
(S,Se)
 
7
][Ag
 
9
Cu(S,Se)
 
2
Se
 
2
]
2.GB.15Cupropearceite
[Cu
 
6
As
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
2.GB.15Cupropolybasite
[Cu
 
6
Sb
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
2.GB.15UM1979-17-S:BiCuFe
Cu
 
18
Fe
 
4
BiS
 
16
2.GB.20Galkhaite
(Cs,Tl)(Hg,Cu,Zn)
 
6
(As,Sb)
 
4
S
 
12
Related Minerals - Hey's Index Grouping:

- +
5.2.1Smithite
AgAsS
 
2
5.2.2Trechmannite
AgAsS
 
2
5.2.3Proustite
Ag
 
3
AsS
 
3
5.2.4Xanthoconite
Ag
 
3
AsS
 
3
5.2.5Pearceite
[(Ag,Cu)
 
6
(As,Sb)
 
2
S
 
7
][Ag
 
9
CuS
 
4
]
5.2.6Pearceite-T2ac
5.2.7Argentotennantite
Ag
 
6
[Cu
 
4
(Fe,Zn)
 
2
]As
 
4
S
 
13
5.2.8Miargyrite
AgSbS
 
2
5.2.9Pyrargyrite
Ag
 
3
SbS
 
3
5.2.10Pyrostilpnite
Ag
 
3
SbS
 
3
5.2.11Stephanite
Ag
 
5
SbS
 
4
5.2.13Billingsleyite
Ag
 
7
AsS
 
6
5.2.14Polybasite-Tac
5.2.15Freibergite
Ag
 
6
[Cu
 
4
Fe
 
2
]Sb
 
4
S
 
13-x
5.2.16Aramayoite
Ag(Sb,Bi)S
 
2
5.2.17Matildite
AgBiS
 
2
5.2.18Schapbachite
Ag
 
0.4
Pb
 
0.2
Bi
 
0.4
S
5.2.19Pavonite
(Ag,Cu)(Bi,Pb)
 
3
S
 
5
5.2.20Arcubisite
Ag
 
6
CuBiS
 
4
5.2.21Bohdanowiczite
AgBiSe
 
2
5.2.22Selenostephanite
Ag
 
5
Sb(Se,S)
 
4
5.2.23Benleonardite
Ag
 
8
(Sb,As)Te
 
2
S
 
3
5.2.24Volynskite
AgBiTe
 
2

Other Names for Polybasite

Other Languages:
German:Eugenglanz
Polybasit
Simplified Chinese:硫锑铜银矿
Spanish:Polybasita

Polytypes for Polybasite

Polytypes:
Polybasite-M2a2b2cPolybasite-T2acPolybasite-Tac

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.
Industrial Uses:Silver ore

References for Polybasite

Reference List:

- +
Penfield (1896), American Journal of Science: 2: 17.

Mügge (1903): 394, 401.

Van Horn (1911), American Journal of Science: 32: 40.

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: 351-353.

D. C. Harris, E. W. Nuffield, and M. H. Frohberg (1965): Studies of mineral sulpho-salts. XIX - Selenian polybasite. Can. Mineral. 8, 172-184.

American Mineralogist (1967): 52: 1311.

Evain, M., L. Bindi and S. Menchetti (2006): Structural complexity in minerals: twinning, polytypism and disorder in the crystal structure of polybasite, (Ag,Cu)16(Sb,As)2S11. Acta Cryst. B62, 447-456.

Bindi, Luca, Michel Evain, Paul G. Spry, and Silvio Menchett (2007) The pearceite-polybasite group of minerals: Crystal chemistry and new nomenclature rules. American Mineralogist, 92, 918-925.

Luca Bindi and Silvio Menchetti (2009): Adding further complexity to the polybasite structure: The role of Ag in the B layer of the -M2a2b2c polytype. American Mineralogist, 94, 151-155.

Welberry, T. R. & Pasciak, M. (2011): Monte Carlo and molecular dynamics simulation of disorder in the Ag+ fast ion conductors pearceite and polybasite. Metallurgical and Materials Transactions A42, 6-13.

Best Localities for Polybasite

Best of Species:Polybasite

Internet Links for Polybasite

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

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