Metacalciouranoite is an extremely rare secondary uranium mineral typically found as an alteration product in oxidized uranium-rich deposits. It is best identified by its distinct yellowish color, greasy luster, and characteristic radioactive nature, often appearing as platy crusts or earthy masses.
Is this metacalciouranoite?
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 metacalciouranoite with a known reference. Metacalciouranoite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Metacalciouranoite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Metacalciouranoite typically shows a greasy luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, granular aggregates.
Often confused with
Metacalciouranoite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Metacalciouranoite leaves yellow, Uranophane leaves pale yellow; luster reads greasy on Metacalciouranoite and vitreous on Uranophane.
How to tell apart: Streak differs — Metacalciouranoite leaves yellow, Autunite leaves pale yellow; luster reads greasy on Metacalciouranoite and pearly on Autunite.
How to tell apart: Luster reads greasy on Metacalciouranoite and adamantine on Becquerelite.
Often found alongside metacalciouranoite
Minerals reported to co-occur with metacalciouranoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Ba)U₂O₇·2H₂O
- Mohs hardness
- 3-4
- Density
- 4.8-5.2 g/cm³
- Streak
- Yellow
- Luster
- Greasy
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals, Granular Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find metacalciouranoite
Classic worldwide localities
- Khovalyg-Aksy, Tuva, Russia
- Tyuya-Muyun, Kyrgyzstan
Field-hunting tip
Look in oxidized zones of uranium deposits country — that is the host setting where metacalciouranoite typically forms. If you start seeing uraninite, calcite, gummite in float, you are in the right ground. Field specimens usually show a platy crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find metacalciouranoite on the map
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