Oursinite is a very rare secondary uranium mineral that typically forms as delicate, needle-like yellow crystals or radial sprays. It is almost exclusively found in association with other rare uranyl minerals in oxidized deposits, making it a highly sought-after but difficult-to-acquire species for radioactive mineral collectors.
Is this oursinite?
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 oursinite with a known reference. Oursinite sits at Mohs 3-3.5, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: pale yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, aggregates, radial.
Often confused with
Oursinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Oursinite leaves yellow, Kasolite leaves pale yellow-brown; luster reads vitreous on Oursinite and subadamantine to greasy, dull to earthy when massive on Kasolite.
How to tell apart: Streak differs, so Oursinite leaves yellow, Boltwoodite leaves white; luster reads vitreous on Oursinite and pearly; radial aggregates vitreous to silky; dull to earthy in microcrystalline pseudomorphs on Boltwoodite.
Often found alongside oursinite
Minerals reported to co-occur with oursinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Co(UO₂)₂(SiO₃OH)₂·6H₂O
- Mohs hardness
- 3-3.5
- Density
- 3.674 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, aggregates, radial
- Cleavage
- On fhk0g
- Fluorescence
- Yellow-green under UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in brecciated dolostone containing uraninite
Where rockhounds find oursinite
Classic worldwide localities
- Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire)
Field-hunting tip
Where it forms: A secondary mineral in brecciated dolostone containing uraninite. If you start seeing soddyite, kasolite, schoepite in float, you are in the right ground. Typical habit: acicular, aggregates, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify oursinite?+
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Find oursinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
