Bournonite is a lead-copper-antimony sulfosalt classically known as “cogwheel ore” (车轮矿) for its distinctive cyclic-twinned crystals that look like geared wheels. It is the single most architecturally distinctive sulfosalt species.
Properties
- Formula: PbCuSbS3
- Crystal system: Orthorhombic
- Hardness: 2.5 – 3
- Color: Steel-gray to iron-black
- Streak: Steel-gray
- Luster: Metallic
- Cleavage: Imperfect on {010}
- Density: 5.7 – 5.9 g/cm³
Occurrence in China
The Yaogangxian mine, Hunan is China’s premier bournonite locality, producing some of the world’s finest cyclic-twinned cogwheel crystals up to several centimeters across, often perched on quartz and chalcopyrite. Historic European localities include Cornwall (UK) and Neudorf (Germany).
Identification
Cyclic six-armed cogwheel twins on (110) are unmistakable when present. Without the twin morphology, distinguish from galena (cubic, brighter), jamesonite (fibrous/needle-like) and tetrahedrite (cubic tetrahedra).
Collector Notes
Bournonite specimens are valued by both metallic-mineral specialists and geometric/architectural-mineral collectors. Yaogangxian and Cornwall pieces top auction catalogs.
Found at these Localities
- Cornwall Mining District (康沃尔矿区)
- Yaogangxian Mine (瑶岗仙矿)
- Hunan (湖南)
