Comparison · Sedimentary Rocks vs Metamorphic Rocks
Shale vs Slate
Shale and Slate are easy to confuse. Slate is harder (Mohs 3.5) than Shale (Mohs 2–3), so Slate will scratch Shale and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Shale and Slate
- Slate is harder (Mohs 3.5) than Shale (Mohs 2–3), so Slate will scratch Shale and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
- Luster is different: Shale is dull to earthy (slightly sub-vitreous if micaceous) while Slate is dull.
- Hold a thin edge to the light: Shale is Opaque, Slate is opaque.
- They overlap in gray, black, red, and green, but Shale also comes in brown and Slate also comes in purple.
Shale vs Slate properties
| Property | Shale | Slate |
|---|---|---|
| Type | Sedimentary Rocks | Metamorphic Rocks |
| Mohs hardness | 2–3 | 3.5 |
| Luster | Dull to earthy (slightly sub-vitreous if micaceous) | dull |
| Streak | — | Variable; test individual minerals |
| Transparency | Opaque | opaque |
| Specific gravity | 2.4–2.8 | 2.8 |
| Crystal system | — | varies |
| Common colors | Gray, Black, Brown, Red, Greenish gray | Gray, Black, Green, Purple, Red |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$100+ |
Which is more valuable?
Typical specimens of Shale and Slate trade in a similar range, around $10.
About Shale
Shale is a fine-grained sedimentary rock formed from compacted clay and silt-sized particles, distinguished by its characteristic fissility, meaning it splits easily into thin, flat layers parallel to its original bedding planes. It accumulates in low-energy environments such as lake bottoms, river deltas, and offshore marine basins where fine sediment can settle undisturbed. Shale is one of the most abundant sedimentary rocks on Earth, making up a substantial portion of the sedimentary rock record worldwide.
About Slate
Slate is a fine-grained metamorphic rock that splits easily into flat sheets. Its durability and water resistance make it ideal for roofing and flooring.
Shale vs Slate FAQ
Is Shale the same as Slate?
No. Shale is a sedimentary rock while Slate is a metamorphic rock. Slate is harder (Mohs 3.5) than Shale (Mohs 2–3), so Slate will scratch Shale and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
How can you tell Shale from Slate?
Slate is harder (Mohs 3.5) than Shale (Mohs 2–3), so Slate will scratch Shale and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Luster is different: Shale is dull to earthy (slightly sub-vitreous if micaceous) while Slate is dull. Hold a thin edge to the light: Shale is Opaque, Slate is opaque.
Which is harder, Shale or Slate?
Slate is harder: Mohs 3.5 against Mohs 2–3 for Shale.
Which is more valuable, Shale or Slate?
Typical specimens of Shale and Slate trade in a similar range, around $10.
