sedimentary
Shale (possibly Carbonaceous or Oil Shale)
Laminated Mudstone (primarily clay minerals and quartz)
Hardness: 3-4 (Mohs); Color: Black to dark gray; Luster: Dull/Earthy; Structure: Fissile/Laminated; Cleavage: Basal (splits into thin sheets); Specific Gravity: 2.2-2.8
- Hardness
- 3-4 (Mohs)
- Color
- Black to dark gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Black to dark gray; Luster: Dull/Earthy; Structure: Fissile/Laminated; Cleavage: Basal (splits into thin sheets); Specific Gravity: 2.2-2.8
Formation & geological history
Formed through the compaction of silt and clay-sized mineral particles over millions of years in low-energy environments like lake beds or deep ocean floors. Black varieties indicate high organic content.
Uses & applications
Used in the production of bricks, cement, and pottery. Bituminous shale can be a source of oil and natural gas (fracking industry).
Geological facts
Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the rocks in the Earth's crust. It often preserves fossils because of the fine sediment size.
Field identification & locations
Identify by its tendency to split into thin layers (fissility) and its soft, earthy texture. It is commonly found in basins and river deltas worldwide.
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