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Chalcocite
Chalcocite is sulfide (copper), Cu₂S. In the hand, it rates 2.5 to 3 on the Mohs scale, and it runs dark lead gray and blue-black. Dark lead-gray heavy copper ore, soft enough to carve with a knife, that takes a sooty black tarnish, richest of the common copper sulfides.
The geology.
Chalcocite carries the formula Cu₂S. It belongs to the monoclinic (pseudo-hexagonal) system. On paper it is sulfide (copper).
It sits at 2.5 to 3 on the Mohs scale. The surface reads metallic, dulling to sooty. Light behaviour is opaque. Specific gravity runs 5.5 to 5.8. The streak is gray-black, shining. It breaks with indistinct cleavage; conchoidal fracture; slightly sectile.
Dark lead-gray heavy copper ore, soft enough to carve with a knife, that takes a sooty black tarnish, richest of the common copper sulfides.
Expect to see it as massive ore chunks, rare tabular crystals or replacement coatings.
The origins.
Enriched zones of copper deposits; notable: Cornwall (England, historic crystals), Montana and Connecticut (USA), Kazakhstan.
On value, the database notes: affordable ore; sharp historic crystals are museum-grade.
Traditional associations.
In energy work traditions, chalcocite has little established lore; copper minerals generally carry energy-conducting themes.
Recorded here because it is part of how this material is sold, not because it is a property of the material.
Spotting the real thing.
Dark lead-gray heavy copper ore, soft enough to carve with a knife, that takes a sooty black tarnish, richest of the common copper sulfides.
| Looks like | How to tell them apart |
|---|---|
| Galena | Galena cleaves into bright cubes; chalcocite is duller with no cubic cleavage |
| Bornite | Bornite tarnishes purple-bronze; chalcocite goes flat sooty black |
| Hematite | Hematite is harder and streaks red-brown |
At-home tests.
None of these need a lab. A 10x loupe, good daylight and a steady hand cover most of what a buyer needs to know about chalcocite.
| Test | What you should see |
|---|---|
| Scratch check | Knife cuts it slightly (sectile) |
| By eye | Heavy (SG ~5.6) |
| By eye | Shining gray-black streak |
If these checks leave you unsure, that is what appraisers are for. Do not file, heat or soak a piece to find out.
Care & handling.
At 2.5 to 3 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with indistinct cleavage; conchoidal fracture; slightly sectile, which is worth knowing before you set it or drop it.
Most damage happens during cleaning, not wearing. Avoid steamers, ultrasonic tanks and anything from under the sink.
Copper sulfide, wash hands after handling crumbly ore.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Cu₂S. Crystal system: Monoclinic (pseudo-hexagonal). Specific gravity: 5.5 to 5.8. Streak: Gray-black, shining. Cleavage and fracture: Indistinct cleavage; conchoidal fracture; slightly sectile.
How it reaches the market
Enriched zones of copper deposits; notable: Cornwall (England, historic crystals), Montana and Connecticut (USA), Kazakhstan.
What it gets confused with
Galena: Galena cleaves into bright cubes; chalcocite is duller with no cubic cleavage. Bornite: Bornite tarnishes purple-bronze; chalcocite goes flat sooty black. Hematite: Hematite is harder and streaks red-brown.
What it is worth
Affordable ore; sharp historic crystals are museum-grade.
One more thing
Chalcocite is nearly 80% copper by weight, miners called rich pockets of it 'copper glance' and treated them like buried treasure.
An education-first guide.
There is nothing to buy on this page. Chalcocite is not part of our catalogue, and the guide is here anyway because somebody searching the name deserves a straight answer.
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