Digenite

Digenite is a copper sulfide mineral with formula: Cu9S5. Digenite is a black to dark blue opaque mineral that crystallizes with a trigonal - hexagonal scalenohedral structure. In habit it is usually massive, but does often show pseudo-cubic forms. It has poor to indistinct cleavage and a brittle fracture. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 5.6. It is found in copper sulfide deposits of both primary and supergene occurrences. It is typically associated with and often intergrown with chalcocite, covellite, djurleite, bornite, chalcopyrite and pyrite.
See more at Wikipedia.org...

General Information:
 Chemical Formula:
Cu9S5
 Composition:
(Molecular Weight = 732.24 gm)
Copper 78.10 % Cu
Sulfur 21.90 % S 
 Empirical Formula:
Cu9S5
 IMA Status:
Approved IMA 1960
Physical Properties:
 Cleavage:
[???] Indistinct
 Color:
blue, dark blue, or black.
 Density:
5.6
 Diaphaniety:
Opaque
 Hardness:
2.5-3 - Finger Nail-Calcite
 Luster:
Sub Metallic
 Streak:
grayish black
More details...