sedimentary
Shale or Siltstone
Sedimentary Rock (Siliciclastic)
Hardness: 3 on Mohs scale; Color: Gray, tan, or buff-colored; Luster: Dull or earthy; Crystal structure: Non-crystalline (fine-grained clastic); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4-2.8
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, or buff-colored
- Luster
- Dull or earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or buff-colored; Luster: Dull or earthy; Crystal structure: Non-crystalline (fine-grained clastic); Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4-2.8
Formation & geological history
Formed through the lithification of mud, clay, and silt particles deposited in low-energy environments like lake beds, floodplains, or marine basins. These rocks can date from any geological period where sedimentation occurred.
Uses & applications
Used primarily as a source of clay for brick and tile manufacturing. It can also be a component in Portland cement and a source for natural gas (shale gas) or oil in specific geological formations.
Geological facts
Shale is the most common sedimentary rock on Earth, making up about 70 percent of the rocks in the Earth's crust. It often contains well-preserved fossils due to the fine grain of the sediment.
Field identification & locations
Identify in the field by its tendency to break into thin, flat sheets (fissility) and its fine, gritty feel if silt is present. Found globally in areas with deep sedimentary basins.
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