Chalcocite is one of the richest copper sulfide ores (~80% Cu by mass) and a critical secondary-enrichment-zone mineral above many copper porphyry and Cu sulfide deposits. It is the cornerstone of the supergene Cu-sulfide chain.
Properties
- Formula: Cu2S
- Crystal system: Orthorhombic (low-T) / hexagonal (high-T)
- Hardness: 2.5 – 3
- Color: Lead-gray to black, often tarnishing blue or green
- Streak: Grayish-black
- Luster: Metallic
- Cleavage: Indistinct on {110}
- Density: 5.5 – 5.8 g/cm³
Occurrence in China
Chalcocite is widespread in the supergene zones of major Chinese Cu deposits: Dexing (Jiangxi), Tonglushan/Daye (Hubei), Pulang and Yangla (Yunnan). Historically Cornwall (UK) and the Bristol Cu mine (Connecticut) produced classic specimens.
Identification
Lead-gray + sectile (cuts like lead) + sometimes pseudo-hexagonal twinned tablets. Distinguish from galena (perfect cubic cleavage, lower hardness-per-density). Chalcocite often has a distinctive bluish tarnish on fresh surfaces.
Collector Notes
Cornwall pseudo-hexagonal chalcocite twins are historical classics. Modern Chinese mines occasionally yield twinned crystals on bornite-chalcopyrite matrix.
Found at these Localities
- Chuquicamata (丘基卡马塔铜矿)
- Boleo District (Santa Rosalía) (圣罗萨利亚博莱奥铜矿区)
- Cornwall Mining District (康沃尔矿区)
- Yangla Copper Mine (羊拉铜矿)
- Pulang Cu Porphyry Mine (普朗铜矿)
- Tonglüshan Bronze-Age Cu Mine (铜绿山古矿)
- Dexing Mine (德兴铜矿)
- Daye District (大冶)
- Hubei (湖北)
- Yunnan (云南)
- Jiangxi (江西)
