sedimentary
Shale
Argillite / Shaly Mudstone
Hardness: 3 on Mohs scale; Color: Gray to brownish; Luster: Dull/Earthy; Structure: Fissile, layered; Cleavage: Perfect along bedding planes.
- Hardness
- 3 on Mohs scale
- Color
- Gray to brownish
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray to brownish; Luster: Dull/Earthy; Structure: Fissile, layered; Cleavage: Perfect along bedding planes.
Formation & geological history
Formed from the compaction of silt and clay-size mineral particles, typically in low-energy environments like lake bottoms, floodplains, or deep ocean floors.
Uses & applications
Used as a raw material for brick, tile, and pottery; also a major source of natural gas and petroleum via hydraulic fracturing.
Geological facts
Shale is the most common sedimentary rock on Earth, making up over 50% of the sedimentary rocks in the crust. Many fossils are found preserved in shale due to the fine-grained sediment.
Field identification & locations
Identifiable by its thin, flat layers that break easily (fissility). Look for it in road cuts, riverbeds, and sedimentary basins worldwide.
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