sedimentary

Shale

Fissile Siliciclastic Sedimentary Rock

Hardness: 3 on Mohs scale; Color: Grey, brown, or tan; Luster: Dull/Earthy; Structure: Laminated and fissile (splits into thin layers); Cleavage: None (cleaves along bedding planes); Grain size: Very fine clay and silt-sized particles.

Hardness: 3 on Mohs scale
Color: Grey, brown, or tan
Luster: Dull/Earthy

Identified April 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the compaction and lithification of silt and clay-sized mineral particles, typically in quiet, low-energy environments like lake beds or deep ocean basins. Geological age varies significantly from billions of years to recent deposits.

Uses & applications

Primary source for brick and tile manufacturing; used in the cement industry; significant as a host rock for natural gas and petroleum (shale gas).

Geological facts

Shale is the most common sedimentary rock on Earth, making up approximately 70% of the sedimentary rock in the Earth's crust. It often contains well-preserved fossils because of its fine grain size.

Field identification & locations

Identify by its 'fissility'—the ability to break into thin, flat plates. It has a smooth, muddy feel when wet. Found in basins and along riverbanks. Collectors look for shale because it is the most likely rock to contain impressions of leaves or small prehistoric life.