Clarkeite is a rare uranium mineral that typically forms as an alteration product of uraninite within pegmatites. It is almost always found in massive or earthy forms, characterized by its distinct reddish-brown color and significant radioactivity.
Is this clarkeite?
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 clarkeite with a known reference. Clarkeite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Clarkeite leaves a yellowish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Clarkeite typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: reddish-brown, brown, yellowish-orange.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: massive, earthy, fine-grained aggregates.
Often confused with
Clarkeite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Uraninite is the harder of the two (Mohs 5-6 vs. 4); streak differs, so Clarkeite leaves yellowish-brown, Uraninite leaves brownish-black to greenish-black; luster reads waxy on Clarkeite and submetallic to dull on Uraninite.
How to tell apart: Clarkeite is noticeably harder (Mohs 4 vs. 2.5); streak differs, so Clarkeite leaves yellowish-brown, Becquerelite leaves yellow; luster reads waxy on Clarkeite and adamantine on Becquerelite.
Often found alongside clarkeite
Minerals reported to co-occur with clarkeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K,Ca,Pb)₂(UO₂)₂O₄·nH₂O
- Mohs hardness
- 4
- Density
- 6.0-6.4 g/cm³
- Streak
- Yellowish-brown
- Luster
- Waxy
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Massive, Earthy, Fine-grained Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Uranium-bearing Pegmatites, Hydrothermal Veins
- Typical price
- $50-300 per specimen
Where rockhounds find clarkeite
Classic worldwide localities
- Spruce Pine, North Carolina, USA
- Shinkolobwe, DR Congo
- Wölsendorf, Germany
Field-hunting tip
Look in uranium-bearing pegmatites, hydrothermal veins country, the host setting where clarkeite typically forms. If you start seeing uraninite, gummite, becquerelite in float, you are in the right ground. Field specimens usually show a massive, earthy, fine-grained aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find clarkeite on the map
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