sedimentary
Shale with Iron Staining
Fissile Mudrock (Sedimentary Rock)
Hardness: 3-4 (Mohs); Color: Dark gray, brownish-red, olive green; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: Fissility (splits into thin layers)
- Hardness
- 3-4 (Mohs)
- Color
- Dark gray, brownish-red, olive green
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Dark gray, brownish-red, olive green; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: Fissility (splits into thin layers)
Formation & geological history
Formed through the compaction and lithification of silt and clay-sized mineral particles. The reddish-orange patches are Likely iron oxides (limonite or hematite) formed by weathering or water interaction.
Uses & applications
Used in the production of bricks, cement, and tiles. Some organic-rich shales are sources of natural gas and oil.
Geological facts
Shale is the most common sedimentary rock on Earth, making up over 50% of the sedimentary rocks in the crust. Many shales contain well-preserved fossils because of their fine-grained nature.
Field identification & locations
Identify in the field by its tendency to split into thin flat plates. It is commonly found in river beds, former lake basins, and coastal areas. It will often feel smooth to the touch unlike sandstone.
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