sedimentary
Shale
Shale (Argillaceous sedimentary rock)
Hardness: 3 on Mohs scale; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Very fine-grained (clay minerals); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
- Hardness
- 3 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Very fine-grained (clay minerals); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8
Formation & geological history
Formed from the compaction of silt and clay-size mineral particles. These sediments typically accumulate in low-energy environments like lake bottoms, river deltas, and floodplains over millions of years.
Uses & applications
Used primarily in the production of cement, bricks, and tiles. Historically significant as a source rock for petroleum and natural gas (shale gas) via hydraulic fracturing.
Geological facts
Shale is the most common sedimentary rock on Earth. Because of its fine-grained nature, it often preserves fossils with incredible detail, including leaves and ancient marine life.
Field identification & locations
Identify by its dark color, earthy smell when wet, and its tendency to split along thin, parallel planes (fissility). It is found globally in sedimentary basins.
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