Fourmarierite is a striking secondary uranium mineral characterized by its vibrant orange-red tabular crystals. It is typically found as an alteration product of uraninite in the oxidized zones of uranium deposits, often occurring in dense, subparallel clusters or crusts.
Is this fourmarierite?
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 fourmarierite with a known reference. Fourmarierite 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. Fourmarierite leaves a orange-yellow streak.
- 3Read the lusterHold the specimen under a strong light. Fourmarierite typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: red, orange, reddish-brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, subparallel aggregates, crusts.
Often confused with
Fourmarierite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Fourmarierite leaves orange-yellow, Becquerelite leaves yellow.
How to tell apart: Streak differs — Fourmarierite leaves orange-yellow, Curite leaves orange.
How to tell apart: Streak differs — Fourmarierite leaves orange-yellow, Vandenbrandeite leaves light green; luster reads adamantine on Fourmarierite and vitreous on Vandenbrandeite.
Often found alongside fourmarierite
Minerals reported to co-occur with fourmarierite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb(UO₂)₄O₃(OH)₄·4H₂O
- Mohs hardness
- 3-4
- Density
- 6.05 g/cm³
- Colors
- Streak
- Orange-yellow
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Subparallel Aggregates, Crusts
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium-bearing Hydrothermal Deposits
- Typical price
- $50-500 thumbnail, $300-2000 cabinet
Where rockhounds find fourmarierite
Classic worldwide localities
- Shinkolobwe mine, DR Congo
- Margnac mine, France
- Gooseberry mine, USA
- Menzenschwand, Germany
Field-hunting tip
Look in oxidized zones of uranium-bearing hydrothermal deposits country — that is the host setting where fourmarierite typically forms. If you start seeing curite, becquerelite, kasolite in float, you are in the right ground. Field specimens usually show a tabular crystals, subparallel aggregates, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fourmarierite on the map
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