Compreignacite is a rare secondary uranium mineral often found as small, yellow, tabular crystal aggregates in oxidized uranium deposits. It is specifically known as a product of the alteration of uraninite and requires careful handling due to its radioactivity.
Is this compreignacite?
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 compreignacite with a known reference. Compreignacite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Compreignacite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Compreignacite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange-yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, crusts, radial aggregates.
Often confused with
Compreignacite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads pearly on Compreignacite and adamantine on Becquerelite.
How to tell apart: Luster reads pearly on Compreignacite and vitreous on Billietite.
How to tell apart: Streak differs — Compreignacite leaves yellow, Masuyite leaves orange-yellow; luster reads pearly on Compreignacite and adamantine on Masuyite.
Often found alongside compreignacite
Minerals reported to co-occur with compreignacite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂[(UO₂)₆O₄(OH)₆]·7H₂O
- Mohs hardness
- 2.5
- Density
- 4.74 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Crusts, Radial Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium-rich Hydrothermal Deposits
- Typical price
- $50-500 depending on specimen size and quality
Where rockhounds find compreignacite
Classic worldwide localities
- Compreignac, Haute-Vienne, France
- Schneeberg, Saxony, Germany
- Katanga, Democratic Republic of the Congo
Field-hunting tip
Look in oxidized zones of uranium-rich hydrothermal deposits country — that is the host setting where compreignacite typically forms. If you start seeing becquerelite, uraninite, gummite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find compreignacite on the map
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