Grundmannite is a rare copper selenide mineral originally discovered in the Harz Mountains of Germany. It is typically found as small, lead-black metallic grains embedded in complex selenium-rich ore assemblages.
Is this grundmannite?
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 grundmannite with a known reference. Grundmannite sits at Mohs 2-2.5, 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: black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: anhedral to subhedral grains.
Often confused with
Grundmannite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Grundmannite leaves black, Clausthalite leaves grayish black.
How to tell apart: Streak differs, so Grundmannite leaves black, Berzelianite leaves shining.
How to tell apart: Cobaltite is the harder of the two (Mohs 5.5 vs. 2-2.5); streak differs, so Grundmannite leaves black, Cobaltite leaves grayish black.
Often found alongside grundmannite
Minerals reported to co-occur with grundmannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuBiSe₂
- Mohs hardness
- 2-2.5
- Density
- 6.582 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Anhedral to subhedral grains
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A primary mineral, deposited from oxidizing low-temperature hydrothermal fluids at the waning stage of selenide formation in a telethermal vein
Where rockhounds find grundmannite
Classic worldwide localities
- El Dragόn selenide occurrence, Cordillera Oriental, Department of Potosí, southwestern Bolivia
Field-hunting tip
Where it forms: A primary mineral, deposited from oxidizing low-temperature hydrothermal fluids at the waning stage of selenide formation in a telethermal vein. If you start seeing watkinsonite, clausthalite, krut’aite-penroseite in float, you are in the right ground. Typical habit: anhedral to subhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
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Find grundmannite on the map
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