Carnotite Identification Guide
Identify carnotite by its bright canary-yellow powdery crust and radioactivity, and distinguish it from other yellow uranium minerals.
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What Carnotite Looks Like
Carnotite is a uranium-vanadium oxide mineral and one of the most important uranium ores. It is unmistakably bright yellow and almost always occurs as soft, earthy crusts and coatings rather than crystals. Caution: carnotite is radioactive — handle minimally, do not inhale dust, and store separately.
- Color: vivid canary-yellow to greenish-yellow (lemon).
- Luster: dull, earthy to slightly pearly.
- Transparency: opaque.
- Habit: powdery crusts, films, and disseminations in sandstone; rare tiny platy crystals.
Step-by-Step Field-ID Checklist
- Note the color: intense, almost fluorescent-looking canary-yellow is the first clue.
- Check the host: carnotite typically impregnates pale sandstone, often around fossil wood or as bright stains.
- Feel the texture: soft, powdery, easily rubbed off (it will stain fingers — use care because it is radioactive).
- Test radioactivity: a Geiger counter reads strongly elevated — diagnostic for a uranium mineral.
- Confirm softness: very low hardness (~2).
Key Diagnostic Tests
- Mohs hardness: about 2 (soft, crumbly).
- Streak: yellow.
- Radioactivity: strongly radioactive — the single best diagnostic.
- Luster: dull, earthy.
- Solubility: soluble in acids.
- Fluorescence: generally does NOT fluoresce strongly under UV (unlike many other uranium minerals such as autunite), which helps narrow it down.
Common Look-Alikes
- Autunite/torbernite: also yellow-green uranium minerals, but autunite fluoresces brilliant green under UV and forms platy crystals; carnotite is powdery and non-fluorescent.
- Tyuyamunite: very similar yellow uranium-vanadium mineral (the calcium analog); essentially indistinguishable by eye, separated by lab analysis.
- Sulfur: yellow but not radioactive, burns with a blue flame, and smells of sulfur.
- Limonite/yellow ochre stains: earthy yellow but not radioactive — the Geiger counter separates them instantly.
Where Carnotite Is Found
Carnotite is classic in the Colorado Plateau (Colorado, Utah, Arizona, New Mexico), where it impregnates sandstones of the Morrison Formation, frequently associated with fossilized wood. Other occurrences include Australia, Kazakhstan, and Congo. It is mined as a major uranium and vanadium ore.
Frequently asked questions
Is carnotite radioactive?
Yes, strongly. Carnotite is a uranium ore and gives a high reading on a Geiger counter. Handle it minimally, avoid breathing its dust, and store it away from living areas.
How can you identify carnotite?
Look for a vivid canary-yellow, soft, powdery crust on pale sandstone that is strongly radioactive, has a yellow streak, and a hardness near 2.
What is the difference between carnotite and autunite?
Both are yellow uranium minerals, but autunite fluoresces brilliant green under UV and forms platy crystals, while carnotite is powdery, earthy, and generally non-fluorescent.
Why is carnotite important?
It is a major ore of both uranium and vanadium, historically central to mining on the Colorado Plateau.