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. Penroseite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Penroseite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, blackish-gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive, granular, or rarely in small cubic crystals.
Often confused with
Penroseite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Penroseite leaves black, Clausthalite leaves gray-black.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 2.5-3); streak differs — 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 — Penroseite leaves black, Cobaltite leaves greyish-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
- 6.5-6.8 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, Granular, Or Rarely in Small Cubic Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins
- Typical price
- $50-300 per specimen
Where rockhounds find penroseite
Classic worldwide localities
- Chareo, Bolivia
- Sierra de Cacheuta, Argentina
- Kuoerzhenkuola, China
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where penroseite typically forms. If you start seeing clausthalite, aguilarite, siderite in float, you are in the right ground. Field specimens usually show a massive, granular, or rarely in small cubic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find penroseite on the map
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