Andersonite is a rare uranyl carbonate mineral known for its striking bright yellow-green fluorescence under ultraviolet light. It typically occurs as small rhombohedral crystals or efflorescent crusts in the oxidized zones of uranium mines. Collectors prize it for its vibrant reaction under UV lighting, though it must be kept in a climate-controlled environment as it is sensitive to humidity.
Is this andersonite?
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 andersonite with a known reference. Andersonite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to pearly.
- 4Match the color rangeCompare against the expected color range: bright yellow green, green.
- 5Look at form & habitCrystal system: trigonal. Typical habit: druse, pseudo cubic, rhombohedral crystals.
Often confused with
Andersonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside andersonite
Minerals reported to co-occur with andersonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Ca(UO₂)(CO₃)₃·6H₂O
- Mohs hardness
- 2.5
- Density
- 2.8 g/cm³
- Colors
- Bright yellow greenGreen
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
- Crystal habit
- Druse, pseudo cubic, rhombohedral crystals
- Cleavage
- Perfect on {0001}
- Fluorescence
- Bright yellow green under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon secondary mineral, formed in the oxidized zone of uranium-bearing hydrothermal polymetallic deposits; may be post-mine, coating walls of mine tunnels
Where rockhounds find andersonite
Classic worldwide localities
- Hillside mine, about 5.5 km north of Bagdad, Eureka district, Yavapai Co., and in the Cameron area, Coconino Co., Arizona, USA
- Grand Co., from the Parco No. 23 mine and Skinny No. 1 mine, southeast of Thompsons, Bumblebee mine, Seven Mile Canyon, Utah, USA
- Emery Co., at the Delta mine, Utah, USA
- San Juan Co., Atomic King No. 2 mine, south of Moab, and nearby mines in Cane Wash, and at the Repete mine, Utah, USA
- Myrthengraben, Semmering Pass, Austria
- Geevor mine, St. Just, Cornwall, England
Field-hunting tip
Where it forms: An uncommon secondary mineral, formed in the oxidized zone of uranium-bearing hydrothermal polymetallic deposits; may be post-mine, coating walls of mine tunnels. If you start seeing schröckingerite, bayleyite, shwartzite in float, you are in the right ground. Typical habit: druse, pseudo cubic, rhombohedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify andersonite?+
Where is andersonite found?+
Is andersonite safe to handle?+
What rocks look like andersonite?+
What minerals are found with andersonite?+
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Find andersonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
