Cuprobismutite is a rare copper-silver-bismuth sulfosalt typically found in hydrothermal polymetallic vein systems. Collectors usually identify it by its dark, metallic appearance and common association with other complex bismuth-bearing sulfides.
Is this cuprobismutite?
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 cuprobismutite with a known reference. Cuprobismutite sits at Mohs 3.5, 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: blue black, gray, dark blue black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, anhedral grains, striated crystals.
Often confused with
Cuprobismutite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Cuprobismutite is noticeably harder (Mohs 3.5 vs. 2-2.5); streak differs, so Cuprobismutite leaves black, Aikinite leaves grayish black.
How to tell apart: Cuprobismutite is noticeably harder (Mohs 3.5 vs. 2).
Often found alongside cuprobismutite
Minerals reported to co-occur with cuprobismutite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₈AgBi₁₃S₂₄
- Mohs hardness
- 3.5
- Density
- 6.36 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive, anhedral grains, striated crystals
- Cleavage
- None observed
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Rare, of hydrothermal origin with other sulfides and sulfosalts
Where rockhounds find cuprobismutite
Classic worldwide localities
- Colorado, from the Missouri mine, Hall’s Valley, Park Co. (type locality), and at Silver Cliff, Custer Co., USA
- Fairfax quarry, Centreville, Fairfax Co., Virginia, USA
- Tunnel Extension 2 mine, Marysvale, Ohio district, Piute Co., Utah, USA
- Krupka, Czech Republic
- Baicolliou, Switzerland
Field-hunting tip
Where it forms: Rare, of hydrothermal origin with other sulfides and sulfosalts. If you start seeing emplectite, aikinite, wittichenite in float, you are in the right ground. Typical habit: massive, anhedral grains, striated crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cuprobismutite?+
Where is cuprobismutite found?+
Is cuprobismutite safe to handle?+
What rocks look like cuprobismutite?+
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Find cuprobismutite on the map
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