Bournonite

Synonyms:  Antimonial Copper Glance, Antimonial Lead Ore, Berthonite,  Cog Wheel Oree, Endellionite, Tripelglanz
Classification:  Sulfides and sulfosalts
Chemical formula:  PbCuSbS3
Crystal system:  Orthorhombic
Density (g/cm3):  5.83 measured, 5.84 calculated
Tenacity:  Brittle
Cleavage:  Imperfect, Fair
Fracture:  Irregular, Uneven, Sub-Conchoidal
Hardness (Mohs):  2,5 - 3
Colour:  Steel-gray
Lustre:  Metallic
Streak:  Steel-gray
Type locality:  Wheal Boys (Trewetha Mine; Old Trewetha Mine), Port Isaac, St Endellion, Wadebridge District, Cornwall, England, UK
Application:  Minor ore of Pb, Cu, Sb