Cleusonite is a rare member of the crichtonite group found primarily in alpine-type veins in Switzerland. It typically occurs as small, black, tabular rhombohedral crystals characterized by their metallic luster and distinct uranium content.
Is this cleusonite?
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 cleusonite with a known reference. Cleusonite sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: bright submetallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular rhombohedral crystals.
Often confused with
Cleusonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads bright submetallic on Cleusonite and metallic to submetallic on Ilmenite.
How to tell apart: Streak differs, so Cleusonite leaves black, Hematite leaves cherry-red or reddish brown; luster reads bright submetallic on Cleusonite and metallic or submetallic to dull on Hematite.
How to tell apart: Cleusonite is noticeably harder (Mohs 6-7 vs. 4.5-5); streak differs, so Cleusonite leaves black, Crichtonite leaves dark gray; luster reads bright submetallic on Cleusonite and metallic, dull to bright on Crichtonite.
Often found alongside cleusonite
Minerals reported to co-occur with cleusonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb(U,U)Fe₂(Ti,Fe,Fe)₁₈(O,OH)₃₈
- Mohs hardness
- 6-7
- Density
- 4.74 g/cm³
- Colors
- Streak
- Black
- Luster
- Bright submetallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Tabular rhombohedral crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In alpine-type cleft veins in greenschist facies metamorphic rocks
Where rockhounds find cleusonite
Classic worldwide localities
- Cleuson, upper Val de Nendaz, and near the Bella Tolla summit, St-Luc, Val d’Anniviers, Valais, Switzerland
- Previously described “uranium-rich senaite” from Alinci, Macedonia and the “plumbodavidite” from Huanglongpu, China are also cleusonite
Field-hunting tip
Where it forms: In alpine-type cleft veins in greenschist facies metamorphic rocks. If you start seeing clausthalite, chalcopyrite, uraninite in float, you are in the right ground. Typical habit: tabular rhombohedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find cleusonite on the map
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