sedimentary
Shale
Shale (Lutite)
Hardness: 3 on Mohs scale; Color: Gray to dark black; Luster: Dull; Crystal structure: Non-crystalline (clastic); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
- Hardness
- 3 on Mohs scale
- Color
- Gray to dark black
- Luster
- Dull
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray to dark black; Luster: Dull; Crystal structure: Non-crystalline (clastic); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
Formation & geological history
Formed through the compaction of silt and clay-sized mineral particles over millions of years, typically in low-energy environments like lake beds or deep ocean floors.
Uses & applications
Used in the production of bricks, tile, and cement. Dark shales are also major sources of natural gas and petroleum via fracking.
Geological facts
Shale is the most common sedimentary rock on Earth. Deeply buried shale is often the source rock for many of the world's hydrocarbon deposits.
Field identification & locations
Identify in the field by its distinct layering and 'fissility', meaning it breaks easily along flat planes. Common in river basins and ancient sea beds.
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