sedimentary
Silty Shale
Silty Shale (Fissile Sedimentary Rock)
Hardness: 3-4 (Mohs); Color: Gray, tan, to black; Luster: Dull/Earthy; Structure: Clastic, fine-grained with visible laminations; Cleavage: Fissile, splits into thin plates or layers; Specific Gravity: 2.4-2.8
- Hardness
- 3-4 (Mohs)
- Color
- Gray, tan, to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Gray, tan, to black; Luster: Dull/Earthy; Structure: Clastic, fine-grained with visible laminations; Cleavage: Fissile, splits into thin plates or layers; Specific Gravity: 2.4-2.8
Formation & geological history
Formed from the compaction and lithification of silt and clay-sized mineral particles. Typically deposited in low-energy environments like river floodplains, lakes, or deep marine basins. Common in Paleozoic and Mesozoic strata.
Uses & applications
Used in the manufacturing of cement, bricks, and tile. Some shales are sources of natural gas or oil (shale gas). Used as fill material in construction.
Geological facts
Shale is the most common sedimentary rock on Earth, making up approximately 70% of the sedimentary rocks in the crust. It often contains well-preserved fossils due to the fine grain size of the sediment.
Field identification & locations
Identify by its 'fissility' - the ability to split into thin flat sheets. It feels gritty if rubbed against teeth (indicating silt content) and does not fizz with acid unless it contains calcite. Commonly found in road cuts and riverbanks.
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