sedimentary
Red Shale
Lutite (primarily composed of Hydrous Aluminum Silicates with Hematite staining)
Hardness: 3 (Mohs scale); Color: Reddish-brown to brick red; Luster: Dull/Earthy; Crystal Structure: Clastic (fine-grained clay minerals); Cleavage: Perfect fissility (breaks into thin layers); Specific Gravity: 2.4-2.8
- Hardness
- 3 (Mohs scale)
- Color
- Reddish-brown to brick red
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Reddish-brown to brick red; Luster: Dull/Earthy; Crystal Structure: Clastic (fine-grained clay minerals); Cleavage: Perfect fissility (breaks into thin layers); Specific Gravity: 2.4-2.8
Formation & geological history
Formed through the lithification of mud and clay particles deposited in calm, oxygen-rich environments like river floodplains or shallow marine basins. The red color indicates the presence of ferric iron (hematite) during formation. Most common in Paleozoic and Mesozoic strata.
Uses & applications
Used primarily in the manufacturing of bricks, terracotta, and cement. It is also processed as a filler in various industrial compounds and used for road base in local construction.
Geological facts
Red shale is a key indicator of terrestrial or shallow-water oxygenated environments. Because it splits so thinly, it is a common host rock for fossilized leaves and insect remains.
Field identification & locations
Identify in the field by its distinct layering (fissility) and soft, earthy texture that can often be scratched with a fingernail. It is common throughout the Appalachian Mountains and the Colorado Plateau. Collectors look for pieces containing fossil impressions.
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