Autunite is a secondary uranium mineral characterized by its striking neon-green fluorescence under UV light. It typically occurs as thin, square-shaped tabular crystals or micaceous crusts in the oxidized zones of uranium deposits.
Is this autunite?
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 autunite with a known reference. Autunite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on {001}.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-green, lemon-yellow, pale yellow, greenish yellow, pale green.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: foliated, micaceous, tabular.
Often confused with
Autunite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Autunite leaves pale yellow, Meta-autunite leaves yellow; luster reads vitreous, pearly on {001} on Autunite and pearly to dull on Meta-autunite.
How to tell apart: Streak differs, so Autunite leaves pale yellow, Uranocircite leaves light yellow; luster reads vitreous, pearly on {001} on Autunite and pearly on Uranocircite.
Often found alongside autunite
Minerals reported to co-occur with autunite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(UO₂)₂(PO₄)₂·10-12H₂O
- Mohs hardness
- 2-2.5
- Density
- 3.05-3.2 g/cm³
- Streak
- Pale yellow
- Luster
- Vitreous, pearly on {001}
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
- Crystal habit
- Foliated, micaceous, tabular
- Cleavage
- Perfect on {001}; {100}, indistinct
- Fluorescence
- Green yellow under SW and LW UV
- Rarity
- Common
- Uses
- Collector
- Host rock
- A secondary mineral derived from primary uranium-bearing minerals under oxidizing conditions, in hydrothermal veins, granite pegmatites, etc
Where rockhounds find autunite
17 mapped spotsClassic worldwide localities
- Dahl (Daybreak) mine, near Mt. Spokane, east of Elk, Spokane Co., Washington, USA
- L’Ouche d’Jau, Saint-Symphorien-de-Marmagne, and the Les Oudots mine, Autun district, Saône-et-Loire, France
- Margnac mine, Compreignac, Haute-Vienne, France
- Gagnol mine, Lachaux, Puy-de-Dôme, France
- Sabugal, Urgeiriça, Portugal
- Peveragno, near Cúneo, Piedmont, Italy
U.S. states with autunite
Each link opens a state-specific list of mapped rockhounding spots that produce autunite.
Field-hunting tip
Where it forms: A secondary mineral derived from primary uranium-bearing minerals under oxidizing conditions, in hydrothermal veins, granite pegmatites, etc. If you start seeing meta-autunite, torbernite, phosphuranylite in float, you are in the right ground. Typical habit: foliated, micaceous, tabular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, North Carolina, Connecticut. Start trip planning there.
More autunite photos
Common questions
How do you identify autunite?+
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Can I find autunite in the United States?+
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Find autunite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
