Hallimondite is a very rare lead uranyl arsenate mineral typically found as small, bright yellow tabular crystals. It is a secondary mineral primarily occurring in the oxidation zones of uranium-bearing hydrothermal deposits, often associated with other rare secondary uranium minerals.
Is this hallimondite?
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 hallimondite with a known reference. Hallimondite 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. Hallimondite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Hallimondite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-orange.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals, tabular.
Often confused with
Hallimondite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Hallimondite leaves yellow, Autunite leaves pale yellow; luster reads vitreous on Hallimondite and pearly on Autunite.
How to tell apart: Streak differs — Hallimondite leaves yellow, Torbernite leaves pale green.
Often found alongside hallimondite
Minerals reported to co-occur with hallimondite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂(UO₂)(AsO₄)₂·nH₂O
- Mohs hardness
- 2-3
- Density
- 4.82 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Platy Crystals, Tabular
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Uranium-bearing Deposits
- Typical price
- $50-300 per specimen depending on size and quality
Where rockhounds find hallimondite
Classic worldwide localities
- Wittichen, Germany
- Saint-Just-près-Brioude, France
Field-hunting tip
Look in hydrothermal veins in uranium-bearing deposits country — that is the host setting where hallimondite typically forms. If you start seeing uraninite, parsonsite, mimetite in float, you are in the right ground. Field specimens usually show a platy crystals, tabular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hallimondite on the map
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