sedimentary
Red Shale
Lutite (primarily composed of clay minerals and iron oxides like hematite, Fe2O3)
Hardness: 2-3 on the Mohs scale; Color: Reddish-brown to terra cotta; Luster: Dull/Earthy; Crystal Structure: Formed of microscopic clay particles with no visible crystals; Cleavage: Fissile (splits easily along bedding planes); Specific Gravity: 2.4 - 2.8
- Hardness
- 2-3 on the Mohs scale
- Color
- Reddish-brown to terra cotta
- Luster
- Dull/Earthy
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Physical properties
Hardness: 2-3 on the Mohs scale; Color: Reddish-brown to terra cotta; Luster: Dull/Earthy; Crystal Structure: Formed of microscopic clay particles with no visible crystals; Cleavage: Fissile (splits easily along bedding planes); Specific Gravity: 2.4 - 2.8
Formation & geological history
Formed through the compaction and cementation of fine-grained silt and clay-sized particles. The red color indicates formation in an oxygen-rich environment (oxidizing conditions), often in floodplain, river delta, or shallow marine settings. They can range from the Proterozoic to the Cenozoic era.
Uses & applications
Used primarily in the manufacturing of bricks, terracotta tiles, and Portland cement. Occasionally used as a filler in paints or as a heavy substrate in landscaping. It is generally not used in jewelry due to its softness.
Geological facts
Red shales are indicative of terrestrial or oxidizing environments, often referred to by geologists as 'Red Beds.' They are excellent for preserving microfossils and sometimes trackway fossils from ancient land creatures.
Field identification & locations
Identify in the field by its characteristic 'fissility' (tendency to break into thin flat layers) and earthy red color. It will not fizz with acid (distinguishing it from limestone) and is soft enough to be scratched by a copper penny or steel nail. Common in the Appalachian Mountains and the Southwestern United States.
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