Wallisite

General Information:
 Chemical Formula:
PbTl(Cu,Ag)As2S5
 Composition:
(Molecular Weight = 796.38 gm)
Thallium 25.66 % Tl
Copper 5.98 % Cu
Silver 3.39 % Ag
Arsenic 18.82 % As
Lead 26.02 % Pb
Sulfur 20.13 % S 
 Empirical Formula:
PbTlCu0.75Ag0.25As2S5
 IMA Status:
Approved IMA 1968
Physical Properties:
 Cleavage:
[111] Good
 Color:
lead gray or black.
 Density:
5.71
 Diaphaniety:
Opaque
 Luster:
Metallic
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