Carrollite

Carrollite is a steely gray mineral found in Carroll County, Maryland. It got its name from the copper ore mines near Sykesville and Finksburg Maryland where it was first found. It consists of a mixture of linnaeite and intergrown copper sulphides. The cobalt in the linnaeite is partly substituted by copper, iron and nickel.
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General Information:
 Chemical Formula:
Cu(Co,Ni)2S4
 Composition:
(Molecular Weight = 309.55 gm)
Cobalt 28.56 % Co
Copper 20.53 % Cu
Nickel 9.48 % Ni
Sulfur 41.43 % S 
 Empirical Formula:
CuCo1.5Ni0.5S4
Physical Properties:
 Cleavage:
[001] Indistinct
 Color:
gray, gray, copper red, light gray, or steel.
 Density:
4.5 - 4.8, Average = 4.65
 Diaphaniety:
Opaque
 Hardness:
4.5-5.5
 Luster:
Metallic
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