Dumontite is a rare secondary uranium phosphate mineral that typically forms bright yellow, bladed or tabular crystals. It is highly sought after by collectors of radioactive minerals due to its attractive color and distinct crystalline habit, usually sourced from classic copper-uranium deposits in the Katanga region of the Congo.
Is this dumontite?
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 dumontite with a known reference. Dumontite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Dumontite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Dumontite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: yellow, amber, brownish-yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: bladed to tabular crystals, sometimes lath-like or radial aggregates.
Often confused with
Dumontite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Dumontite leaves yellow, Autunite leaves pale yellow; luster reads resinous on Dumontite and pearly on Autunite.
How to tell apart: Streak differs — Dumontite leaves yellow, Parsonsite leaves white; luster reads resinous on Dumontite and adamantine on Parsonsite.
How to tell apart: Streak differs — Dumontite leaves yellow, Torbernite leaves pale green; luster reads resinous on Dumontite and vitreous on Torbernite.
Often found alongside dumontite
Minerals reported to co-occur with dumontite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂[(UO₂)₃O₂(PO₄)₂]·5H₂O
- Mohs hardness
- 3
- Density
- 5.3 g/cm³
- Streak
- Yellow
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Bladed to Tabular Crystals, Sometimes Lath-like or Radial Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium-bearing Hydrothermal Deposits
- Typical price
- $50-500 thumbnail
Where rockhounds find dumontite
Classic worldwide localities
- Shinkolobwe Mine, Democratic Republic of the Congo
- Musonoi Mine, Democratic Republic of the Congo
- Litchi, France
Field-hunting tip
Look in oxidized zones of uranium-bearing hydrothermal deposits country — that is the host setting where dumontite typically forms. If you start seeing uraninite, parsonsite, saleeite in float, you are in the right ground. Field specimens usually show a bladed to tabular crystals, sometimes lath-like or radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find dumontite on the map
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