Calciouranoite is an extremely rare secondary uranium mineral typically found as an alteration product of uraninite. It occurs most commonly as bright yellow earthy masses or crusts within oxidized zones of uranium ore bodies.
Is this calciouranoite?
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 calciouranoite with a known reference. Calciouranoite 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: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy to dull.
- 4Match the color rangeCompare against the expected color range: brown, orange, orange brown, red orange.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular, prismatic, radial.
Often confused with
Calciouranoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Calciouranoite is noticeably harder (Mohs 4 vs. 2.5); streak differs, so Calciouranoite leaves yellow, Uranophane leaves yellowish white; luster reads greasy to dull on Calciouranoite and vitreous on Uranophane.
How to tell apart: Streak differs, so Calciouranoite leaves yellow, Boltwoodite leaves white; luster reads greasy to dull on Calciouranoite and pearly; radial aggregates vitreous to silky; dull to earthy in microcrystalline pseudomorphs on Boltwoodite.
Often found alongside calciouranoite
Minerals reported to co-occur with calciouranoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Ba,Pb,K,Na)U₂O₇·5H₂O
- Mohs hardness
- 4
- Density
- 4.62 g/cm³
- Streak
- Yellow
- Luster
- Greasy to dull
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Acicular, prismatic, radial
- Cleavage
- One direction, pinacoidal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In stringers in felsite, deep in the oxidation zone of a U–Mo deposit, in water-saturated ore-bearing faults
Where rockhounds find calciouranoite
Classic worldwide localities
- Oktyabr’skoye U–Mo deposit, 12 km southeast of Krasnokamensk, eastern Transbaikal, Russia
Field-hunting tip
Where it forms: In stringers in felsite, deep in the oxidation zone of a U–Mo deposit, in water-saturated ore-bearing faults. If you start seeing calcite, uranophane, bauranoite in float, you are in the right ground. Typical habit: acicular, prismatic, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify calciouranoite?+
Where is calciouranoite found?+
Is calciouranoite safe to handle?+
What rocks look like calciouranoite?+
What minerals are found with calciouranoite?+
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Find calciouranoite on the map
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