Uranosphaerite is a rare secondary uranium mineral that typically forms distinct orange, spherical, or globular radiating crystal aggregates. It is most commonly found in historical bismuth-uranium mining districts in Europe, often associated with altered uraninite. Due to its radioactive nature and scarcity, it is sought after primarily by advanced mineral collectors specializing in uranium or bismuth species.
Is this uranosphaerite?
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 uranosphaerite with a known reference. Uranosphaerite 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.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy.
- 4Match the color rangeCompare against the expected color range: orange, red orange, brick red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: botryoidal, radial.
Often confused with
Uranosphaerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Uranosphaerite leaves yellow, Uranophane leaves yellowish white; luster reads greasy on Uranosphaerite and vitreous on Uranophane.
How to tell apart: Streak differs, so Uranosphaerite leaves yellow, Boltwoodite leaves white; luster reads greasy on Uranosphaerite and pearly; radial aggregates vitreous to silky; dull to earthy in microcrystalline pseudomorphs on Boltwoodite.
Often found alongside uranosphaerite
Minerals reported to co-occur with uranosphaerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Bi(UO₂)O₂OH
- Mohs hardness
- 2-3
- Density
- 6.36 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Greasy
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Botryoidal, radial
- Cleavage
- {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An oxidation product of uraninite in a Co-Ni-Bi-bearing hydrothermal vein (Schneeberg, Germany)
Where rockhounds find uranosphaerite
Classic worldwide localities
- Walpurgis vein, Weisser Hirsch mine, Neustädtl, near Schneeberg, Saxony and from the Clara mine, Black Forest, Germany
- Kersegalec, near Lignol, Morbihan, France
Field-hunting tip
Where it forms: An oxidation product of uraninite in a Co-Ni-Bi-bearing hydrothermal vein (Schneeberg, Germany). If you start seeing walpurgite, uranospinite, uranospathite in float, you are in the right ground. Typical habit: botryoidal, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify uranosphaerite?+
Where is uranosphaerite found?+
Is uranosphaerite safe to handle?+
What rocks look like uranosphaerite?+
What minerals are found with uranosphaerite?+
What kind of rock does uranosphaerite form in?+
What is uranosphaerite used for?+
Find uranosphaerite on the map
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