RocksdayKaolinite vs Sepiolite
How to tell them apart
A white clay mineral formed when feldspar weathers. It's the main ingredient of porcelain.
Photo: James St. John https://www.flickr.com/people/jsjgeology?rb=1, CC BY 2.0
A soft, porous clay mineral that's light enough to float when dry. It's carved into meerschaum pipes.
Photo: Shannon Heinle, CC0
Quick tests
- Heft: Kaolinite feels noticeably heavier for its size (specific gravity 2.6 vs 2).
Key differences
- Kaolinite is a clay that turns plastic when wet.
Side by side
| Property | Kaolinite | Sepiolite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 2–2.5 | 2–2.5 |
| Luster | Earthy | Dull to earthy |
| Streak | White | White |
| Colors | White, Yellow, Pink | White, Yellow, Gray |
| Crystal system | Triclinic | Orthorhombic |
| Specific gravity | 2.6 | 2 |
| Formula | Al₂Si₂O₅(OH)₄ | Mg₄Si₆O₁₅(OH)₂·6H₂O |
| Found in | Jingdezhen, China; Cornwall, England | Eskişehir, Turkey; Spain |
Properties that are the same for both are grayed out.
How to identify kaolinite
- White, chalky and powdery.
- Smells earthy when breathed on and gets plastic when wet.
- Doesn't fizz in acid.
Crystal system: Triclinic
Full Kaolinite guide →How to identify sepiolite
- White to cream, chalky and very light.
- Sticks to the tongue.
- Easily carved with a knife.
Crystal system: Orthorhombic
Full Sepiolite guide →More comparisons
Could you tell them apart from a blurry close-up?
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