sedimentary

Shale

Lutaceous Rock (Sedimentary Mudrock)

Hardness: 3 (Mohs Scale), Color: Grey to black, Luster: Dull/Earthy, Structure: Fine-grained clastic with fissile bedding (thin layers), Cleavage: Parallel to bedding plane, Specific Gravity: 2.4-2.8

Identified June 10, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs Scale), Color: Grey to black, Luster: Dull/Earthy, Structure: Fine-grained clastic with fissile bedding (thin layers), Cleavage: Parallel to bedding plane, Specific Gravity: 2.4-2.8

Formation & geological history

Formed through the compaction and lithification of silt and clay-size mineral particles (mud) in calm environments such as lake bottoms, river deltas, or deep ocean floors over millions of years.

Uses & applications

Used in the production of cement, bricks, and tiles. It is also a significant source of natural gas and petroleum (shale gas) via hydraulic fracturing.

Geological facts

Shale is the most common sedimentary rock on Earth, making up about 70 percent of the rocks in the Earth's crust. It often preserves fossils with incredible detail due to its fine grain size.

Field identification & locations

Identify in the field by its tendency to break into thin, flat plates (fissility) and its soft, clay-like feel when wet. Commonly found in basins where slow-moving water once deposited fine sediments.