sedimentary

Shale

Shale (claystone/mudstone)

Hardness: 3 on Mohs scale; Color: Red-brown (due to iron oxide); Luster: Dull/Earthy; Structure: Fissile, meaning it splits into thin flat layers; Cleavage: No true cleavage but exhibits bedding planes.

Hardness: 3 on Mohs scale
Color: Red-brown (due to iron oxide)
Luster: Dull/Earthy

Identified June 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the compaction of silt and clay-sized mineral particles, commonly in low-energy environments like river deltas, floodplains, and lake bottoms. Formation can span millions of years.

Uses & applications

Used in the manufacture of bricks, ceramics, and cement. It is also a significant source rock for oil and natural gas (shale gas) via hydraulic fracturing.

Geological facts

Red shale gets its distinctive color from hematite (iron oxide). It is the most common sedimentary rock on Earth, making up about 70% of the sedimentary rock in the Earth's crust.

Field identification & locations

Identify in the field by its tendency to break into thin sheets and its smooth, fine-grained texture. It will not scratch glass. It is commonly found in basins worldwide.