Penroseite is a rare nickel selenide mineral that forms part of the pyrite group. It is typically found in hydrothermal veins associated with other selenium minerals, often appearing as massive or granular dark gray masses.
Is this penroseite?
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 penroseite with a known reference. Penroseite 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: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic, tarnishes rapidly.
- 4Match the color rangeCompare against the expected color range: lead gray, steel gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: columnar, radial, reniform.
Often confused with
Penroseite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Penroseite leaves black, Clausthalite leaves grayish black.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 2.5-3); streak differs, so Penroseite leaves black, Pyrite leaves greenish black to brownish black.
How to tell apart: Cobaltite is the harder of the two (Mohs 5.5 vs. 2.5-3); streak differs, so Penroseite leaves black, Cobaltite leaves grayish black.
Often found alongside penroseite
Minerals reported to co-occur with penroseite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ni,Co,Cu)Se₂
- Mohs hardness
- 2.5-3
- Density
- 6.58-6.74 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic, tarnishes rapidly
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Columnar, radial, reniform
- Cleavage
- Perfect on {001}; distinct on {011}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In hydrothermal veins
Where rockhounds find penroseite
Classic worldwide localities
- Pacajake mine, Hiaco, 24 km east-northeast of Colquechaca, Potosí, Bolivia (type locality)
- Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire)
- Hope’s Nose, Torquay, Devon, England
- Harz Mountains, at Tilkerode, Germany
- Kuusamo, northeastern Finland
Field-hunting tip
Where it forms: In hydrothermal veins. If you start seeing naumannite, clausthalite, gersdorffite in float, you are in the right ground. Typical habit: columnar, radial, reniform. Train your eye for that shape before scanning the outcrop.
Common questions
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Find penroseite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
