sedimentary

Shale

Clastic Sedimentary Rock

Hardness: 3 on the Mohs scale. Color: Brown, gray, black, red, or green. Luster: Dull or earthy. Crystal structure: None (amorphous/microcrystalline clay minerals). Cleavage: Well-developed platy cleavage (fissility), splitting easily into thin layers. Specific gravity: 2.0 to 2.8.

Hardness: 3 on the Mohs scale
Color: Brown, gray, black, red, or green
Luster: Dull or earthy

Identified July 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the compaction of silt and clay-size mineral particles (mud) accumulating in quiet depositional environments such as deep marine basins, lagoons, or lakes over millions of years.

Uses & applications

Used in the manufacture of bricks, tiles, and pottery; as a raw material for cement production; and increasingly as a source of shale gas through hydraulic fracturing.

Geological facts

Shale is the most abundant sedimentary rock on Earth, making up over 70 percent of sedimentary rock crust. Under intense heat and pressure, shale transforms into slate through metamorphism.

Field identification & locations

Identified easily by its fine-grained texture, layered bedding, and tendency to break into thin, brittle flakes. Commonly found worldwide in sedimentary basins.