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 — 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 — 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 — that is 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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