sedimentary

Shale

Shale (clastic sedimentary rock composed of silt and clay-sized particles)

Hardness: 3 on Mohs scale; Color: Gray, black, or reddish-brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline/fine-grained; Cleavage: Fissile (splits into thin layers); Specific gravity: 2.4 - 2.8

Hardness: 3 on Mohs scale
Color: Gray, black, or reddish-brown
Luster: Dull/Earthy

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the compaction and lithification of silt and clay mineral particles. Typically deposited in low-energy environments such as lakes, river deltas, floodplains, and offshore marine basins. Geological age varies from Precambrian to Cenozoic.

Uses & applications

Used as a source of fossil fuels (oil shale), as a component in ceramics, bricks, and cement production, and as a filler in paint and plastics.

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 is often a primary source of natural gas through fracking.

Field identification & locations

Identify in the field by its fine grain size (grains too small to see with the naked eye) and its tendency to split into thin, flat plates (fissility). It is commonly found in basins and ancient lake beds worldwide.

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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