Chalcocite is a major copper ore mineral often found in secondary enrichment zones of copper deposits. It is easily recognized by its dark lead-gray color, which frequently develops a dull or iridescent blue-purple tarnish upon exposure to air.
Is this chalcocite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch chalcocite with a known reference. Chalcocite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: blackish lead-gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: lead-gray, black, tarnish-blue, tarnish-iridescent, blue black, gray, black gray, steel gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: euhedral crystals, granular, massive.
Often confused with
Chalcocite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Chalcocite leaves blackish lead-gray, Bornite leaves pale grayish black.
How to tell apart: Streak differs, so Chalcocite leaves blackish lead-gray, Galena leaves lead-gray.
How to tell apart: Streak differs, so Chalcocite leaves blackish lead-gray, Covellite leaves lead-gray, shining; luster reads metallic on Chalcocite and submetallic, inclining to resinous, somewhat pearly on cleavage; subresinous to dull when massive on Covellite.
Often found alongside chalcocite
Minerals reported to co-occur with chalcocite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂S
- Mohs hardness
- 2.5-3
- Density
- 5.5-5.8 g/cm³
- Colors
- Streak
- Blackish lead-gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Euhedral crystals, granular, massive
- Cleavage
- Indistinct on {110}
- Rarity
- Common
- Uses
- Ore of copper, Collector
- Host rock
- An uncommon primary hydrothermal mineral but important as a secondary mineral
Where rockhounds find chalcocite
33 mapped spotsClassic worldwide localities
- Bristol, Hartford Co., Connecticut, USA
- Bisbee, Cochise Co., Arizona, USA
- Magma mine, Superior, Pinal Co., Arizona, USA
- United Verde Extension mine, Yavapai Co., Arizona, USA
- Turinsk copper mine, Bogoslovsk, Ural Mountains, Russia
- Cornwall at St. Just, St. Ives, Camborne, and Redruth, England
U.S. states with chalcocite
Each link opens a state-specific list of mapped rockhounding spots that produce chalcocite.
Field-hunting tip
Where it forms: An uncommon primary hydrothermal mineral but important as a secondary mineral. If you start seeing pyrite, chalcopyrite, covellite in float, you are in the right ground. Typical habit: euhedral crystals, granular, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, New Mexico, Connecticut. Start trip planning there.
More chalcocite photos
Common questions
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Find chalcocite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
