RocksdayCoal vs Shale
How to tell them apart
A rock formed from buried, compressed plant material — ancient swamp forests turned to stone.
Photo: Amcyrus2012, CC BY 4.0
Compacted mud and clay that splits into thin layers. The most common sedimentary rock.
Photo: James St. John, CC BY 2.0
Quick tests
- Heft: Shale feels noticeably heavier for its size (specific gravity 2.4–2.8 vs 1.1–1.8).
Key differences
- Black shale is heavier and won't burn.
Side by side
| Property | Coal | Shale |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 2–3 | 3 |
| Luster | Dull to submetallic | Dull |
| Colors | Black, Brown | Gray, Black, Red, Green |
| Crystal system / structure | Organic, layered | Clastic, very fine, splits in layers |
| Specific gravity | 1.1–1.8 | 2.4–2.8 |
| Found in | Powder River Basin, Wyoming; Appalachia | Burgess Shale, British Columbia; Marcellus, Pennsylvania |
Properties that are the same for both are grayed out.
How to identify coal
- Black and very light for a rock.
- Leaves black dust on hands.
- Layered, with blocky or curved breaks.
- Burns.
Structure: Organic, layered
Full Coal 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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