Bournonite
Image: Didier Descouens (CC BY-SA 4.0)
Mineral NameBournonite
Chemical FormulaPbCuSbS3
Mohs Hardness2.5
Crystal Systemorthorhombic
Lustermetallic
Streak Colorsteel-gray to black
Cleavagedistinct on {010}, indistinct on {100} and {001}
Fractureuneven to sub-conchoidal
Specific Gravity5.8
Colorssteel-gray, lead-gray, iron-black
Transparencyopaque
Type LocalityLes Malines, Saint-Laurent-le-Minier, Gard France
Mineral GroupSulfosalts
Usesminor ore of lead, copper, and antimony, collector
Associated Mineralsgalena, sphalerite, tetrahedrite, chalcopyrite, pyrite, quartz, baryte, siderite
Rarityuncommon
Description
This specimen showcases a classic 'cog wheel' twin of dark, steel-gray bournonite crystals with a metallic luster, prominently displayed on a matrix of white, bladed crystals (likely baryte) and a grey host rock.
Geological Context
Bournonite forms in hydrothermal veins, typically in low to moderate temperature environments associated with lead-zinc-silver deposits, often found alongside other sulfide minerals.
