RocksdayShale vs Slate
How to tell them apart
Compacted mud and clay that splits into thin layers. The most common sedimentary rock.
Photo: James St. John, CC BY 2.0
Shale transformed by low-grade metamorphism into a hard rock that splits into smooth, flat sheets.
Photo: Dexter Perkins, CC0
Key differences
- Slate is harder and rings when tapped; shale gives a dull thud.
- Shale is softer, crumbly and thuds when tapped.
Side by side
| Property | Shale | Slate |
|---|---|---|
| Type | Sedimentary rock | Metamorphic rock |
| Mohs hardness | 3 | 3–4 |
| Luster | Dull | Dull to faint sheen |
| Colors | Gray, Black, Red, Green | Gray, Black, Green, Purple |
| Crystal system / structure | Clastic, very fine, splits in layers | Very fine, foliated (slaty cleavage) |
| Specific gravity | 2.4–2.8 | 2.7–2.8 |
| Found in | Burgess Shale, British Columbia; Marcellus, Pennsylvania | Gwynedd, Wales; Slate Valley, Vermont–New York |
Properties that are the same for both are grayed out.
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 →How to identify slate
- Splits into thin, flat, smooth sheets.
- Rings when tapped.
- Harder than shale.
- Grains invisible.
Structure: Very fine, foliated (slaty cleavage)
Full Slate guide →More comparisons
Could you tell them apart from a blurry close-up?
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