sedimentary
Shale with Iron Staining
Fissile Argillaceous Sedimentary Rock
Hardness: 3 on Mohs scale; Color: Gray to black with reddish-brown iron oxide patches; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: Fissile (splits into thin layers).
- Hardness
- 3 on Mohs scale
- Color
- Gray to black with reddish-brown iron oxide patches
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray to black with reddish-brown iron oxide patches; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: Fissile (splits into thin layers).
Formation & geological history
Formed from the compaction of silt and clay-sized mineral particles in low-energy environments like lake beds or deep ocean floors. The reddish staining occurs via secondary oxidation of iron-bearing minerals during weathering.
Uses & applications
Used in the production of cement, bricks, and tile. Historically significant as a source rock for hydrocarbons (natural gas and oil).
Geological facts
Shale is the most common sedimentary rock on Earth. It often contains microfossils and is critical for understanding past climate conditions and sea-level changes.
Field identification & locations
Identify by its ability to split into thin sheets (fissility) and its fine texture. Found globally in sedimentary basins. Collectors often look for fossil impressions on the bedding planes.
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