sedimentary

Shale

Argillaceous sedimentary rock

Hardness: 3 on Mohs scale; Color: Gray, black, or dark brown; Luster: Dull/earthy; Crystal Structure: Very fine-grained (clastic); Cleavage: Perfect fissility, breaks into thin flat layers.

Hardness: 3 on Mohs scale
Color: Gray, black, or dark brown
Luster: Dull/earthy

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, black, or dark brown; Luster: Dull/earthy; Crystal Structure: Very fine-grained (clastic); Cleavage: Perfect fissility, breaks into thin flat layers.

Formation & geological history

Formed from the compaction of silt and clay-size mineral particles (mud) in low-energy environments like lake bottoms, river deltas, or floodplains over millions of years.

Uses & applications

Used in the production of cement, bricks, and tiles. It is also an important source rock for oil and natural gas (shale gas) via hydraulic fracturing.

Geological facts

Shale is the most common sedimentary rock on Earth, making up about 70 percent of all sedimentary rocks in the crust.

Field identification & locations

Identify by its ability to split into thin, flat plates (fissility) and its soft, clay-like smell when wet. Often found in areas with historical water activity and layered outcroppings.