Tyuyamunite is a secondary uranium vanadate mineral that typically forms as bright yellow earthy crusts or thin platy crystal aggregates. It is frequently found in sandstone-hosted uranium deposits within the Colorado Plateau and is highly valued by mineral collectors for its intense fluorescence under short-wave UV.
Is this tyuyamunite?
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 tyuyamunite with a known reference. Tyuyamunite 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: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine, pearly on {001}, may be dull to waxy if massive.
- 4Match the color rangeCompare against the expected color range: yellow, greenish yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: earthy, platy, scaly.
Often confused with
Tyuyamunite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tyuyamunite leaves light yellow, Carnotite leaves strontian-yellow; luster reads adamantine, pearly on {001}, may be dull to waxy if massive on Tyuyamunite and dull, earthy; silky when crystalline on Carnotite.
How to tell apart: Streak differs, so Tyuyamunite leaves light yellow, Autunite leaves pale yellow; luster reads adamantine, pearly on {001}, may be dull to waxy if massive on Tyuyamunite and vitreous, pearly on {001} on Autunite.
How to tell apart: Luster reads adamantine, pearly on {001}, may be dull to waxy if massive on Tyuyamunite and pearly on Uranocircite.
Often found alongside tyuyamunite
Minerals reported to co-occur with tyuyamunite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(UO₂)₂(VO₄)₂·5-8H₂O
- Mohs hardness
- ~2
- Density
- 3.57-4.35 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Adamantine, pearly on {001}, may be dull to waxy if massive
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Earthy, platy, scaly
- Cleavage
- On {001}, perfect, micaceous; on {100}, {010}, distinct
- Fluorescence
- Weak yellow-green under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector, Uranium ore
- Host rock
- An uncommon mineral in the oxidized zone of U–V deposits, especially those of the Colorado Plateau-type
Where rockhounds find tyuyamunite
Classic worldwide localities
- Jackpile mine, Laguna district, Cibola Co., and at a number of mines in the Grants district, New Mexico, USA
- Paradox Valley, Montrose Co., Calamity Creek, Mesa Co., Colorado, USA
- Monument No. 2 mine, Monument Valley, Apache Co., in the Ridenaur breccia pipe, Coconino Co., Arizona, USA
- Gold Quarry mine, near Carlin, Eureka Co., Nevada, USA
- Tyuya-Muyun Cave, Fergana Valley, Alai Range, Kyrgyzstan
- West Wheal Owles, St. Just, Cornwall, England
Field-hunting tip
Where it forms: An uncommon mineral in the oxidized zone of U–V deposits, especially those of the Colorado Plateau-type. If you start seeing metatyuyamunite, carnotite, corvusite in float, you are in the right ground. Typical habit: earthy, platy, scaly. Train your eye for that shape before scanning the outcrop.
Common questions
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