Kruťaite is a rare copper selenide mineral typically found as small, metallic grains within hydrothermal veins. It is most famously associated with the uranium deposits at Bukov and Predborice in the Czech Republic, where it occurs alongside other rare selenides.
Is this kruťaite?
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 kruťaite with a known reference. Kruťaite 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: dark gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: inclusions.
Often confused with
Kruťaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 4); streak differs, so Kruťaite leaves dark gray, Pyrite leaves greenish black to brownish black.
How to tell apart: Marcasite is the harder of the two (Mohs 6-6.5 vs. 4); streak differs, so Kruťaite leaves dark gray, Marcasite leaves grayish or brownish black.
Often found alongside kruťaite
Minerals reported to co-occur with kruťaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuSe₂
- Mohs hardness
- 4
- Density
- 6.53 g/cm³
- Colors
- Streak
- Dark gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Inclusions
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Of hydrothermal origin
Where rockhounds find kruťaite
Classic worldwide localities
- Petrovice uranium deposit, near Ždǎr (type locality) and at Slavkovice, Czech Republic
- El Dragón mine, Potosí, Bolivia
- Tuminico, Sierra de Cacho, and at Los Llantenes, La Rioja Province, Argentina
Field-hunting tip
Where it forms: Of hydrothermal origin. If you start seeing clausthalite, eskebornite, uraninite in float, you are in the right ground. Typical habit: inclusions. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kruťaite?+
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Find kruťaite on the map
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