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Polybasite

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Formula:
[(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]
System:
Monoclinic
Colour:
Black with dark ruby ...
Lustre:
Metallic
Hardness:
2½ - 3
Member of:
Name:
From the Greek πολύς, poly, "many" and βάσις, basis, "a base" in allusion to the many base elements present.
Isostructural with:
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

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
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
3.1.7.2

3 : SULFOSALTS
1 : ø > 4
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

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:
6.1 g/cm3 (Measured)    6.36 g/cm3 (Calculated)

Crystallography of Polybasite

Polytype:
Formula:
Crystal System:
Class (H-M)
Space Group:
Space Group Setting:
Cell Parameters:
Ratio:
Unit Cell Volume (calc):
Z:
Polybasite-M2a2b2cPolybasite-T2acPolybasite-Tac
   
  Monoclinic 
2/m - Prismatic
  B2/m
  C2/m



   
   
   

Crystallographic forms of Polybasite

Crystal Atlas:
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Polybasite no.4 - Goldschmidt (1913-1926)
Polybasite no.5 - Goldschmidt (1913-1926)
Polybasite - Tabular {001}
Polybasite - Tabular {001}
3d models and HTML5 code kindly provided by www.smorf.nl.

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Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

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Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation
X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
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)2S7][Ag9CuS4]
Essential elements:
All elements listed in formula:
Common Impurities:
As,Fe

Relationship of Polybasite to other Species

Series:
Forms a series with Pearceite (see here)
Member of:
Other Members of Group:
Cupropearceite[Cu6As2S7][Ag9CuS4]
Cupropolybasite[Cu6Sb2S7][Ag9CuS4]
Pearceite[(Ag,Cu)6(As,Sb)2S7][Ag9CuS4]
Selenopolybasite[(Ag,Cu)6(Sb,As)2(S,Se)7][Ag9Cu(S,Se)2Se2]
2.GB.05ArgentotennantiteAg6[Cu4(Fe,Zn)2]As4S13
2.GB.05FreibergiteAg6[Cu4Fe2]Sb4S13-x
2.GB.05GirauditeCu6[Cu4(Fe,Zn)2]As4Se13
2.GB.05GoldfielditeCu10Te4S13
2.GB.05HakiteCu6[Cu4Hg2]Sb4Se13
2.GB.05TennantiteCu6[Cu4(Fe,Zn)2]As4S13
2.GB.05TetrahedriteCu6[Cu4(Fe,Zn)2]Sb4S13
2.GB.10SelenostephaniteAg5Sb(Se,S)4
2.GB.10StephaniteAg5SbS4
2.GB.15Pearceite[(Ag,Cu)6(As,Sb)2S7][Ag9CuS4]
2.GB.15UM2003-14-S:AgBiFeTeAg16FeBiTe3S8
2.GB.15Selenopolybasite[(Ag,Cu)6(Sb,As)2(S,Se)7][Ag9Cu(S,Se)2Se2]
2.GB.15Cupropearceite[Cu6As2S7][Ag9CuS4]
2.GB.15Cupropolybasite[Cu6Sb2S7][Ag9CuS4]
2.GB.15UM1979-17-S:BiCuFeCu18Fe4BiS16
2.GB.20Galkhaite(Cs,Tl)(Hg,Cu,Zn)6(As,Sb)4S12
5.2.1SmithiteAgAsS2
5.2.2TrechmanniteAgAsS2
5.2.3ProustiteAg3AsS3
5.2.4XanthoconiteAg3AsS3
5.2.5Pearceite[(Ag,Cu)6(As,Sb)2S7][Ag9CuS4]
5.2.6Pearceite-T2ac
5.2.7ArgentotennantiteAg6[Cu4(Fe,Zn)2]As4S13
5.2.8MiargyriteAgSbS2
5.2.9PyrargyriteAg3SbS3
5.2.10PyrostilpniteAg3SbS3
5.2.11StephaniteAg5SbS4
5.2.13BillingsleyiteAg7AsS6
5.2.14Polybasite-Tac
5.2.15FreibergiteAg6[Cu4Fe2]Sb4S13-x
5.2.16AramayoiteAg(Sb,Bi)S2
5.2.17MatilditeAgBiS2
5.2.18SchapbachiteAg0.4Pb0.2Bi0.4S
5.2.19Pavonite(Ag,Cu)(Bi,Pb)3S5
5.2.20ArcubisiteAg6CuBiS4
5.2.21BohdanowicziteAgBiSe2
5.2.22SelenostephaniteAg5Sb(Se,S)4
5.2.23BenleonarditeAg8(Sb,As)Te2S3
5.2.24VolynskiteAgBiTe2

Other Names for Polybasite

Name in Other Languages:
Simplified Chinese:硫锑铜银矿
Spanish:Polybasita

Other Information

Health Risks:
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.

Internet Links for Polybasite

Specimens:
The following Polybasite specimens are currently listed for sale on minfind.com.

Localities for Polybasite

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Mineral and/or Locality  
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