Cliffordite is a rare uranium tellurite mineral typically found as small, brilliant yellow octahedral crystals in oxidized ore zones. Because of its radioactive and toxic nature, it is highly sought after by advanced mineral collectors specializing in tellurium species.
Is this cliffordite?
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 cliffordite with a known reference. Cliffordite 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. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: yellow, sulfur yellow.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, often with rounded faces or striations.
Often confused with
Cliffordite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Cliffordite leaves light yellow, Empressite leaves gray-black to black; luster reads adamantine on Cliffordite and metallic on Empressite.
How to tell apart: Cliffordite is noticeably harder (Mohs 4 vs. 2); streak differs, so Cliffordite leaves light yellow, Tellurite leaves white; luster reads adamantine on Cliffordite and subadamantine on Tellurite.
Often found alongside cliffordite
Minerals reported to co-occur with cliffordite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- UTe₃O₉
- Mohs hardness
- 4
- Density
- 6.57 g/cm³
- Colors
- YellowSulfur yellow
- Streak
- Light yellow
- Luster
- Adamantine
- Transparency
- Semitransparent
- Crystal system
- Cubic
- Crystal habit
- Octahedral crystals, often with rounded faces or striations
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- As rare incrustations along fractures in the oxidized zone of hydrothermal Au–Ag telluride deposits
Where rockhounds find cliffordite
Classic worldwide localities
- San Miguel prospect, and 10 km southeast at the Moctezuma (Bambolla) mine, 12 km south of Moctezuma, Sonora, Mexico
Field-hunting tip
Where it forms: As rare incrustations along fractures in the oxidized zone of hydrothermal Au–Ag telluride deposits. If you start seeing mackayite, barite, quartz in float, you are in the right ground. Typical habit: octahedral crystals, often with rounded faces or striations. Train your eye for that shape before scanning the outcrop.
Common questions
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Find cliffordite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
