Phosphuranylite is a rare secondary uranium phosphate that typically forms as vibrant yellow earthy crusts or thin coatings on other uranium minerals. Collectors should look for its strong yellow-green fluorescence under UV light, which is a key diagnostic feature. It is strictly for advanced collectors who are equipped to handle radioactive materials safely.
Is this phosphuranylite?
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 phosphuranylite with a known reference. Phosphuranylite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to pearly.
- 4Match the color rangeCompare against the expected color range: golden yellow, dark yellow, lemon.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: encrustations, prismatic.
Often confused with
Phosphuranylite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Phosphuranylite leaves light yellow, Autunite leaves pale yellow.
How to tell apart: Streak differs, so Phosphuranylite leaves light yellow, Torbernite leaves pale green.
How to tell apart: Curite is the harder of the two (Mohs 4-5 vs. 2-2.5); streak differs, so Phosphuranylite leaves light yellow, Curite leaves orange; luster reads vitreous to pearly on Phosphuranylite and adamantine on Curite.
Often found alongside phosphuranylite
Minerals reported to co-occur with phosphuranylite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KCa(H₃O)₃(UO₂)₇(PO₄)₄O₄·8H₂O
- Mohs hardness
- 2-2.5
- Density
- 4.1 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Vitreous to pearly
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Encrustations, prismatic
- Cleavage
- Perfect on {100}; indistinct on {010}
- Fluorescence
- Orange-brown under SW UV; Orange-Brown under LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- A secondary mineral typically occurring in the weathering zone of granite pegmatites, coating cracks and fissures near altered uraninite; in paleochannels in sandstone Colorado Plateau-type U–V deposits
Where rockhounds find phosphuranylite
Classic worldwide localities
- Flat Rock and Buchanan pegmatite mines, Mitchell Co., North Carolina, USA
- Ruggles mine, near Grafton, and the Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Newry, Oxford Co., Maine, USA
- Branchville, Fairfield Co., Connecticut, USA
- Énio and Córrego do Urucum pegmatites, near Galiléia, Minas Gerais, Brazil
- Perus district, 25 km north of São Paulo, Brazil
Field-hunting tip
Where it forms: A secondary mineral typically occurring in the weathering zone of granite pegmatites, coating cracks and fissures near altered uraninite; in paleochannels in sandstone Colorado Plateau-type U–V deposits. If you start seeing uraninite, autunite, meta-autunite in float, you are in the right ground. Typical habit: encrustations, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify phosphuranylite?+
Where is phosphuranylite found?+
Is phosphuranylite safe to handle?+
What rocks look like phosphuranylite?+
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Find phosphuranylite on the map
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