sedimentary

Shale

Argillaceous Sedimentary Rock

Hardness: 3 on Mohs scale; Color: Gray to olive-green; Luster: Dull/Earthy; Crystal structure: Microcrystalline clastic; Cleavage: Fissility (splits into thin layers); Specific gravity: 2.4-2.8

Hardness: 3 on Mohs scale
Color: Gray to olive-green
Luster: Dull/Earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray to olive-green; Luster: Dull/Earthy; Crystal structure: Microcrystalline clastic; Cleavage: Fissility (splits into thin layers); Specific gravity: 2.4-2.8

Formation & geological history

Formed by the compaction of silt and clay-size mineral particles, commonly called mud. It forms in low-energy environments like lake beds, river deltas, and floodplains where fine particles can settle out of the water.

Uses & applications

Used as a raw material for brick, pottery, and tile manufacturing. It is also a primary source of natural gas and oil through 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 frequently preserves fossils because of the fine-grained nature of the sediment.

Field identification & locations

Identify in the field by its tendency to break into thin flat pieces (fissility) and its soft, earthy texture. It is often found in riverbanks and road cuts in sedimentary basins.