Boltwoodite is a striking, bright yellow uranium silicate typically found as delicate, fibrous, or acicular radiating sprays. Collectors prize these vivid, radioactive clusters, which are almost exclusively found as secondary minerals in the oxidized zones of uranium-rich ore deposits.
Is this boltwoodite?
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 boltwoodite with a known reference. Boltwoodite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Boltwoodite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Boltwoodite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: yellow, golden yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular or fibrous radial sprays.
Often confused with
Boltwoodite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Boltwoodite is noticeably harder (Mohs 3.5 vs. 2.5); streak differs — Boltwoodite leaves yellow, Uranophane leaves pale yellow; luster reads pearly on Boltwoodite and vitreous on Uranophane.
How to tell apart: Luster reads pearly on Boltwoodite and greasy on Kasolite.
Often found alongside boltwoodite
Minerals reported to co-occur with boltwoodite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na)(UO₂)(SiO₃OH)·1.5H₂O
- Mohs hardness
- 3.5
- Density
- 3.6-3.7 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or Fibrous Radial Sprays
- Cleavage
- Perfect
- Fluorescence
- Bright Yellow-green Under UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Uranium Deposits
- Typical price
- $20-200 depending on specimen size and quality
Where rockhounds find boltwoodite
1 mapped spotsClassic worldwide localities
- Delta Mine, Utah, USA
- Goose Creek, Utah, USA
- Rössing, Namibia
- Shinkolobwe, DR Congo
Field-hunting tip
Look in oxidized uranium deposits country — that is the host setting where boltwoodite typically forms. If you start seeing uraninite, gypsum, fluorite in float, you are in the right ground. Field specimens usually show a acicular or fibrous radial sprays habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California — start trip planning there.
Common questions
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Find boltwoodite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
