Umohoite is a rare secondary uranium mineral typically found as small, black, platy crystals or foliated masses with a distinct pearly luster. It is specifically associated with uranium-molybdenum hydrothermal vein systems. Collectors should handle it with care due to its significant radioactive nature.
Is this umohoite?
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 umohoite with a known reference. Umohoite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: blue gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black, bluish black, dark green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy, rosette, tabular.
Often confused with
Umohoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Umohoite leaves blue gray, Molybdenite leaves bluish gray; luster reads vitreous on Umohoite and metallic on Molybdenite.
How to tell apart: Coffinite is the harder of the two (Mohs 5-6 vs. 2); streak differs, so Umohoite leaves blue gray, Coffinite leaves grayish black; luster reads vitreous on Umohoite and dull to adamantine on Coffinite.
Often found alongside umohoite
Minerals reported to co-occur with umohoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (UO₂)MoO₄·2H₂O
- Mohs hardness
- 2
- Density
- 4.53-4.66 g/cm³
- Streak
- Blue gray
- Luster
- Vitreous
- Transparency
- Semitransparent to opaque
- Crystal system
- Triclinic
- Crystal habit
- Platy, rosette, tabular
- Cleavage
- On {001}, perfect
- Rarity
- Rare
- Uses
- Collector, Scientific study
- Host rock
- A rare secondary mineral, typically in sediment-hosted uranium-bearing deposits, formed in the oxidation zone above the water table
Where rockhounds find umohoite
Classic worldwide localities
- Freedom No. 2 mine, Marysvale, Ohio district, Piute Co., Utah, USA
- Lucky Mc mine, Gas Hills, Fremont Co., Wyoming, USA
- Alyce Tolino mine, Cameron district, Coconino Co., Arizona, USA
- Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire)
- Rabéjac and Mas-d’Alary uranium deposits, south of Lodève, Hérault, France
- Kyzylsai Mo–U deposit, Chu-Ili Mountains, southwestern Balkhash region, Kazakhstan
Field-hunting tip
Where it forms: A rare secondary mineral, typically in sediment-hosted uranium-bearing deposits, formed in the oxidation zone above the water table. If you start seeing uraninite, ilsemannite, jordisite in float, you are in the right ground. Typical habit: platy, rosette, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find umohoite on the map
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