sedimentary
Shale
Fissile mudstone (rich in clay minerals and quartz)
Hardness: 3 on Mohs scale; Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Microcrystalline; Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
- Hardness
- 3 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Microcrystalline; Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
Formation & geological history
Formed through the lithification of mud and silt deposits in low-energy environments like lake beds, river deltas, and deep ocean basins. Primarily from the Silurian to Devonian periods.
Uses & applications
Used in the production of bricks, tiles, and pottery. It is a major source rock for natural gas and petroleum (shale gas/oil), and crushed shale is used as road fill.
Geological facts
Shale is the most common sedimentary rock on Earth, making up over 50% of the sedimentary rocks in the crust. Many shales contain perfectly preserved fossils because of the fine-grained nature of the sediment.
Field identification & locations
Identify by its tendency to break along flat planes (fissility) and its soft, fine-grained texture. It often smells earthy when wet. Commonly found in basins or stacked in thin, crumbly layers in road cuts.
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Shale or Slaty Mudstone
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