sedimentary
Shale
Shale (Consolidated fine-grained clay/silt)
Hardness: 3 on Mohs scale; Color: Gray, black, or brown; Luster: Dull; Crystal structure: Non-crystalline visible particles; Cleavage: Fissile (splits into layers); Specific Gravity: 2.4-2.8
- Hardness
- 3 on Mohs scale
- Color
- Gray, black, or brown
- Luster
- Dull
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, black, or brown; Luster: Dull; Crystal structure: Non-crystalline visible particles; Cleavage: Fissile (splits into layers); Specific Gravity: 2.4-2.8
Formation & geological history
Formed through the compaction and lithification of silt and clay-sized mineral particles, typically in calm water environments such as lake bottoms, floodplains, or deep oceans.
Uses & applications
Used in the production of bricks, tiles, and pottery; a source of natural gas (shale gas) and oil; and crushed for use as sub-base material in road construction.
Geological facts
Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the crust's sedimentary rocks. Fossil preservation is often excellent in fine-grained shales.
Field identification & locations
Identify by its fine-grained texture and its tendency to break into thin, flat plates (fissility). Commonly found in sedimentary basins worldwide. Rubbing it between teeth may feel smoother than sandier siltstones.
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