Mineral Information and Data:

Baumhauerite-2a
Ag1.5Pb22As33.5S72 [CNMNC approved formula]

Named as the monoclinic polymorph of baumhauerite.

IMA status : Approved Species 1990 (IMA1988-051)
CLASSIFICATION 
Dana
(8th edition) :
03.06.13.02  
  (03) Sulfides - Sulfosalts
  (03.06) where 2 < z/y < 2.49 - (A+)i (A++)j [By Cz], A=metals, B=semi-metals, C=non-metals
  (03.06.13)
  
Nickel-Strunz
(10th edition) :
02.HC.05b
  (02) Sulfides
  (02.H) Sulfosalts of SnS Archetype
  (02.HC) With only Pb
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 44.74(4) Å, b = 8.477(4) Å, c = 7.910(6) Å; β = 93.37(5)°
Crystal Habit: As domains intergrown with baumhauerite.
  
Color: Steel-gray
Diaphaneity: Opaque
Luster: Metallic
Hardness (Mohs): 3
Measured Density: 5.31–5.37 (calculated) g/cm3
Cleavage: One perfect, probably {100}
Tenacity: Brittle
Fracture: Conchoidal
Streak: Dark reddish brown
  
Geologic Setting: In sugary dolomite (Binntal, Switzerland)
Mineral Association: Baumhauerite, other lead sulfarsenides, realgar, pyrite, dolomite (Binntal, Switzerland)
  

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