Krupkaite is a rare lead-copper-bismuth sulfide that typically forms as lead-gray, acicular or fibrous needle-like crystals. It is most commonly identified in hydrothermal tin-tungsten deposits, often occurring in intimate intergrowths with other bismuth sulfosalts. Because of its microscopic nature and similarity to other bismuth minerals, precise identification usually requires X-ray diffraction or electron microprobe analysis.
Is this krupkaite?
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 krupkaite with a known reference. Krupkaite sits at Mohs 4, 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: dark steel gray, steel gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous.
Often confused with
Krupkaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Krupkaite is noticeably harder (Mohs 4 vs. 2-2.5); streak differs, so Krupkaite leaves black, Bismuthinite leaves lead-gray.
How to tell apart: Krupkaite is noticeably harder (Mohs 4 vs. 2-2.5); streak differs, so Krupkaite leaves black, Aikinite leaves grayish black.
How to tell apart: Krupkaite is noticeably harder (Mohs 4 vs. 2-3).
Often found alongside krupkaite
Minerals reported to co-occur with krupkaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- PbCuBi₃S₆
- Mohs hardness
- 4
- Density
- 6.98 g/cm³
- Colors
- Dark steel graySteel gray
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous
- Cleavage
- Good on {010}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Rare in hydrothermal veins
Where rockhounds find krupkaite
Classic worldwide localities
- Cucomungo Spring, Tule Canyon district, Esmeralda Co., Nevada, USA
- Ball’s mine, Little Cottonwood district, Salt Lake Co., Utah, USA
- Alice mine, Alice district, Clear Creek Co., Colorado, USA
- Barbora gallery, Krupka, Krušné hory Mountains (type locality) and at Bohutin, near Příbram, Czech Republic
- Dobšiná (Dobschau), Slovakia
- Baia Borşa, Baia Mare (Nagybánya), Romania
Field-hunting tip
Where it forms: Rare in hydrothermal veins. If you start seeing gladite, bismuthinite, aikinite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
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Find krupkaite on the map
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