Uranopilite is a secondary uranium sulfate mineral that typically forms as bright yellow, velvety efflorescences on uranium-bearing rocks. It is highly radioactive and recognizable by its intense, vibrant fluorescence under ultraviolet light.
Is this uranopilite?
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 uranopilite with a known reference. Uranopilite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: lemon, straw yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, reniform.
Often confused with
Uranopilite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Uranopilite and vitreous, pearly on {001} on Autunite.
How to tell apart: Streak differs, so Uranopilite leaves pale yellow, Zippeite leaves yellow white; luster reads silky on Uranopilite and vitreous on Zippeite.
Often found alongside uranopilite
Minerals reported to co-occur with uranopilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (UO₂)₆(SO₄)O₂(OH)₆·14H₂O
- Mohs hardness
- 2.5
- Density
- 3.7-4.0 g/cm³
- Colors
- Streak
- Pale yellow
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, reniform
- Cleavage
- On {010}, perfect
- Fluorescence
- Bright greenish yellow under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- A locally abundant secondary mineral formed under acid conditions by the oxidation of sulfides in the presence of uraninite; may be of post-mining origin
Where rockhounds find uranopilite
Classic worldwide localities
- Found at many localities in the Uravan district, Montrose Co., Colorado, USA
- Happy Jack and Jomac mines, White Canyon district, San Juan Co., and at Capitol Wash, Wayne Co., Utah, USA
- Jáchymov (Joachimsthal) and Příbram, Czech Republic
- Johanngeorgenstadt, Saxony, Germany
- Mas-d’Alary uranium deposit, three km south-southeast of Lodève, Hérault, at La Crouzille, Haute-Vienne, and from Grury, Saône-et-Loire, France
- Wheal Owles, Wheal Edward, and the Geevor mine, St. Just, Cornwall, England
Field-hunting tip
Where it forms: A locally abundant secondary mineral formed under acid conditions by the oxidation of sulfides in the presence of uraninite; may be of post-mining origin. If you start seeing uraninite, zippeite, johannite in float, you are in the right ground. Typical habit: encrustations, reniform. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify uranopilite?+
Where is uranopilite found?+
Is uranopilite safe to handle?+
What rocks look like uranopilite?+
What minerals are found with uranopilite?+
What kind of rock does uranopilite form in?+
What is uranopilite used for?+
Find uranopilite on the map
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