Hauerite

Hauerite is a manganese sulfide mineral: MnS2. It forms reddish brown or black octahedral crystals and it is usually found associated with the sulfides of other transition metals such as rambergite. It was discovered in Austria and named after the mineralogists, J.R. Hauer and F. Hauer.
See more at Wikipedia.org...

(n.)
Native sulphide of manganese a reddish brown or brownish black mineral.
  

General Information:
 Chemical Formula:
MnS2
 Composition:
(Molecular Weight = 119.07 gm)
Manganese 46.14 % Mn
Sulfur 53.86 % S 
 Empirical Formula:
Mn2+S2
 Name Origin:
Named after the Austrian geologists, J. R. Hauer (1778-1863) and F. R. Hauer (1822-1899).
Physical Properties:
 Cleavage:
[100] Perfect, [010] Perfect, [001] Perfect
 Color:
blackish gray, brownish gray, or brownish black.
 Density:
3.463
 Diaphaniety:
Opaque
 Habits:
Euhedral Crystals - Occurs as well-formed crystals showing good external form., Massive - Granular - Common texture observed in granite and other igneous rock.,
 Hardness:
4 - Fluorite
 Luster:
Metallic
 Streak:
reddish brown
More details...