Carrollite is a rare copper-cobalt sulfide that typically forms distinct, metallic octahedral crystals. Collectors prize it for its bright luster and classic isometric crystal habits found primarily in the Copperbelt region of the Congo.
Is this carrollite?
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 carrollite with a known reference. Carrollite sits at Mohs 4.5-5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray, copper red, light gray, steel.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, often with curved faces, or massive.
Often confused with
Carrollite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Carrollite leaves black, Linnaeite leaves grayish black.
How to tell apart: Streak differs, so Carrollite leaves black, Siegenite leaves grayish black.
How to tell apart: Streak differs, so Carrollite leaves black, Pyrite leaves greenish black to brownish black.
Often found alongside carrollite
Minerals reported to co-occur with carrollite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuCo₂S₄
- Mohs hardness
- 4.5-5.5
- Density
- 4.5-4.8 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral crystals, often with curved faces, or massive
- Cleavage
- {001}, imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In hydrothermal vein deposits
Where rockhounds find carrollite
Classic worldwide localities
- Carroll Co., Maryland, in the Patapsco mine, Finksburg (type locality), and the Mineral Hill mine, Sykesville, USA
- Boleo, Baja California, Mexico
- Carrizal Alto copper district, Atacama, Chile
- Chernomorets, Burgas, Bulgaria
- Vysna Boca, Nizke Tatry Mountains, Slovakia
- Kohlenbach mine, near Eiserfeld, and throughout the Siegerland district, North Rhine-Westphalia, Germany
Field-hunting tip
Where it forms: In hydrothermal vein deposits. If you start seeing tetrahedrite, linnaeite, siegenite in float, you are in the right ground. Typical habit: octahedral crystals, often with curved faces, or massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find carrollite on the map
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