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 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow to ocher-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous.
- 4Match the color rangeCompare against the expected color range: golden yellow, light 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, so Dumontite leaves yellow to ocher-yellow, Autunite leaves pale yellow; luster reads resinous on Dumontite and vitreous, pearly on {001} on Autunite.
How to tell apart: Streak differs, so Dumontite leaves yellow to ocher-yellow, Parsonsite leaves white; luster reads resinous on Dumontite and subadamantine to slightly greasy on Parsonsite.
How to tell apart: Streak differs, so Dumontite leaves yellow to ocher-yellow, Torbernite leaves pale green; luster reads resinous on Dumontite and vitreous, subadamantine, waxy, pearly on cleavages; becoming dull on dehydration to metatorbernite 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
- 2-3
- Density
- 5.65 g/cm³
- Streak
- Yellow to ocher-yellow
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Bladed to tabular crystals, sometimes lath-like or radial aggregates
- Cleavage
- Perfect
- Fluorescence
- Weak green under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In pockets of torbernite in the oxidized zone of a uranium deposit (Shinkolobwe, Congo)
Where rockhounds find dumontite
Classic worldwide localities
- White Oak property, near Nogales, Santa Cruz Co., Arizona, USA
- Green Monster and Desert Valley mines, Goodsprings district, Clark Co., Nevada, USA
- Shinkolobwe, Katanga (Shaba) Province, and at the Kobokobo pegmatite, Lusungu River district, Kivu Province, Congo (Zaire)
- South Alligator Valley, and in the Ranger mine, Jabiru, Northern Territory, Australia
Field-hunting tip
Where it forms: In pockets of torbernite in the oxidized zone of a uranium deposit (Shinkolobwe, Congo). If you start seeing torbernite, uranophane, kasolite in float, you are in the right ground. Typical habit: bladed to tabular crystals, sometimes lath-like or radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find dumontite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
