RocksdayMudstone vs Shale
How to tell them apart
Hardened mud that breaks into blocks rather than thin sheets.
Photo: James St. John, CC BY 2.0
Compacted mud and clay that splits into thin layers. The most common sedimentary rock.
Photo: James St. John, CC BY 2.0
Key differences
- Shale splits into thin layers.
Side by side
| Property | Mudstone | Shale |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 2–3 | 3 |
| Luster | Dull | Dull |
| Colors | Gray, Red, Black, Brown | Gray, Black, Red, Green |
| Crystal system / structure | Clastic, clay and silt, blocky | Clastic, very fine, splits in layers |
| Specific gravity | 2.3–2.7 | 2.4–2.8 |
| Found in | Sedimentary basins worldwide; Gale crater, Mars | Burgess Shale, British Columbia; Marcellus, Pennsylvania |
Properties that are the same for both are grayed out.
How to identify mudstone
- Smooth, very fine-grained.
- Breaks into blocky chunks.
- Soft; may smell earthy when wet.
Structure: Clastic, clay and silt, blocky
Full Mudstone guide →How to identify shale
- Splits into thin, flat flakes along its layers.
- Grains too small to see.
- Smells earthy when wet.
- Soft and crumbly at edges.
Structure: Clastic, very fine, splits in layers
Full Shale guide →More comparisons
Could you tell them apart from a blurry close-up?
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