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 4-4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: slightly waxy.
- 4Match the color rangeCompare against the expected color range: reddish brown, brown, brownish yellow, dark brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive.
Often confused with
Clarkeite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Clarkeite leaves yellowish brown, Uraninite leaves brownish black, gray, olive-green, shining; luster reads slightly waxy on Clarkeite and submetallic to greasy, dull on Uraninite.
How to tell apart: Clarkeite is noticeably harder (Mohs 4-4.5 vs. 2.5); streak differs, so Clarkeite leaves yellowish brown, Becquerelite leaves yellow; luster reads slightly waxy on Clarkeite and adamantine to greasy 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(UO₂)O(OH)·nH₂O
- Mohs hardness
- 4-4.5
- Density
- 6.29-6.39 g/cm³
- Streak
- Yellowish brown
- Luster
- Slightly waxy
- Transparency
- Opaque, transparent in thin grains
- Crystal system
- Trigonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Replacing uraninite, as a late-stage hydrothermal alteration product
Where rockhounds find clarkeite
Classic worldwide localities
- Spruce Pine district, from the Deer Park and other mines, Mitchell Co., and the Fanny Gouge mine, Yancey Co., North Carolina, USA
- Ajmer district, Rajputana, India
Field-hunting tip
Where it forms: Replacing uraninite, as a late-stage hydrothermal alteration product. If you start seeing uraninite, uranophane, wölsendorfite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify clarkeite?+
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Find clarkeite on the map
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