Fontanite is a rare uranyl carbonate mineral typically found as secondary crusts or delicate platy crystals in uranium deposits. It is recognized by its soft, pearly appearance and association with other secondary uranium minerals like autunite.
Is this fontanite?
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 fontanite with a known reference. Fontanite sits at Mohs 2-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fontanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fontanite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellowish.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, crusts, aggregates.
Often confused with
Fontanite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Fontanite leaves white, Schröckingerite leaves pale yellow.
How to tell apart: Streak differs — Fontanite leaves white, Liebigite leaves pale yellow; luster reads pearly on Fontanite and vitreous on Liebigite.
Often found alongside fontanite
Minerals reported to co-occur with fontanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(UO₂)₃(CO₃)₂(OH)₄·3H₂O
- Mohs hardness
- 2-3
- Density
- 2.8 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals, Crusts, Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium-bearing Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find fontanite
Classic worldwide localities
- Rabéjac mine, France
- Margnac mine, France
- Lodève, France
Field-hunting tip
Look in oxidized zones of uranium-bearing deposits country — that is the host setting where fontanite typically forms. If you start seeing uraninite, autunite, calcite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts, aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fontanite on the map
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