Gauthierite is an exceptionally rare potassium-lead uranyl oxide mineral discovered in the oxidized zones of uranium mines. It typically occurs as delicate, bright yellow tabular crystals that are highly sought after by collectors of radioactive minerals due to its distinct crystallography.
Is this gauthierite?
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 gauthierite with a known reference. Gauthierite 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. Streak: light orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellowish orange.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, clusters.
Often confused with
Gauthierite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gauthierite leaves light orange, Becquerelite leaves yellow; luster reads vitreous on Gauthierite and adamantine to greasy on Becquerelite.
How to tell apart: Streak differs, so Gauthierite leaves light orange, Curite leaves orange; luster reads vitreous on Gauthierite and adamantine on Curite.
How to tell apart: Streak differs, so Gauthierite leaves light orange, Masuyite leaves orange-yellow.
Often found alongside gauthierite
Minerals reported to co-occur with gauthierite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KPb[(UO₂)₇O₅(OH)₇]·8H₂O
- Mohs hardness
- 3-4
- Density
- 5.437 g/cm³
- Colors
- Streak
- Light orange
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, clusters
- Cleavage
- Perfect on {010}
- Fluorescence
- Bright yellow-green under UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A product of the oxidation-hydration weathering of uraninite and presumably formed by the combination of radiogenic lead and uranium from altered uraninite with potassium leached from gangue minerals
Where rockhounds find gauthierite
Classic worldwide localities
- Found at the Shinkolobwe Mine, Democratic Republic of Congo, Africa
Field-hunting tip
Where it forms: A product of the oxidation-hydration weathering of uraninite and presumably formed by the combination of radiogenic lead and uranium from altered uraninite with potassium leached from gangue minerals. If you start seeing uraninite, quartz, soddyite in float, you are in the right ground. Typical habit: tabular crystals, clusters. Train your eye for that shape before scanning the outcrop.
Common questions
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Find gauthierite on the map
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