sedimentary
Red Shale
Fissile Siliciclastic Sedimentary Rock
Hardness: 3 on Mohs scale; Color: Reddish-brown to maroon due to iron oxide (hematite); Luster: Dull/Earthy; Structure: Fine-grained, fissile (splits into thin layers); Cleavage: Perfect parallel to bedding planes.
- Hardness
- 3 on Mohs scale
- Color
- Reddish-brown to maroon due to iron oxide (hematite)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Reddish-brown to maroon due to iron oxide (hematite); Luster: Dull/Earthy; Structure: Fine-grained, fissile (splits into thin layers); Cleavage: Perfect parallel to bedding planes.
Formation & geological history
Formed through the compaction of silt and clay-sized mineral particles over millions of years. The red color indicates formation in an oxygen-rich environment, typically in floodplains or shallow lake basins where iron was oxidized.
Uses & applications
Used in the manufacturing of bricks, terracotta tiles, and cement. In crushed form, it is used as road base or fill material. High-quality clay-rich shales are also used in ceramics.
Geological facts
Shale is the most common sedimentary rock on Earth, accounting for about 70 percent of the rocks in the Earth's crust. Red shales are often associated with fossils of land plants or tracks because they form in terrestrial or near-shore environments.
Field identification & locations
Identify in the field by its distinct layering and tendency to flake apart into flat plates. It will not fizz with acid (distinguishing it from limestone) and is soft enough to be scratched by a copper penny. Found abundantly in the Appalachian Mountains and the Southwestern United States.
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