Stibnite

Lustre: Metallic.
Hardness: Mohs 2 — soft; a knife will scratch it.
Streak: Lead grey.
Habit: Orthorhombic crystal system.

Colour	Gray, Black
Mohs hardness	2
Lustre	Metallic
Streak	Lead grey
Crystal system	Orthorhombic
Transparency	Opaque
Cleavage	Perfect and easy on {010}; imperfect on {100} and {110}
Fracture	Subconchoidal
Chemical formula	Sb 2 S 3
Specific gravity	4.63

What is Stibnite?

Stibnite, sometimes called antimonite, is a sulfide mineral, a mineral form of antimony trisulfide (Sb2S3). It is a soft, metallic grey crystalline solid with an orthorhombic space group. It is the most important source for the metalloid antimony. The name is derived from the Greek στίβι stibi through the Latin stibium as the former name for the mineral and the element antimony.