RocksdayClaystone vs Kaolinite
How to tell them apart
Rock made mainly of clay minerals: soft, smooth and slick when wet.
Photo: James St. John, CC BY 2.0
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
Quick tests
- Texture: Claystone is a rock — a mix of grains or minerals; Kaolinite is a single mineral.
Key differences
- Kaolinite is a single white clay mineral.
Side by side
| Property | Claystone | Kaolinite |
|---|---|---|
| Type | Sedimentary rock | Mineral |
| Mohs hardness | 1.5–2.5 | 2–2.5 |
| Luster | Dull, earthy | Earthy |
| Streak | — | White |
| Colors | Gray, Red, Green, Brown | White, Yellow, Pink |
| Crystal system / structure | Clastic, clay-sized | Triclinic |
| Specific gravity | 2–2.6 | 2.6 |
| Formula | — | Al₂Si₂O₅(OH)₄ |
| Found in | Sedimentary basins worldwide | Jingdezhen, China; Cornwall, England |
Properties that are the same for both are grayed out.
How to identify claystone
- Very smooth, soapy when wet.
- Scratched by a fingernail.
- Swells or slakes in water.
Structure: Clastic, clay-sized
Full Claystone guide →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 →More comparisons
Could you tell them apart from a blurry close-up?
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