Stibnite, Antimony Sulphide,
Formula Sb2S3.

Crystal system: Orthorhombic (usually forming long prismatic crystals often as attractive radial sprays).
Hardness: 2
Density: 4.6 gms/cm3
Colour: Silvery to black.
Streak: Grey to black.

Stibnite is found in low-temperature thermal veins, often in association with realgar and/or orpiment. When freshly exposed it has bright silvery crystals but these tend to dull to a lead colour over time.  It readily oxydises to stibiconite [formula Sb3O6(OH)] a whitish powder. Some of the finest crystalline specimens come from Hunan Province in China.

The specimen shown comes from Baia Sprie, Romania.

Stibnite from Baia Sprie, Romania.