sedimentary

Shale (or Mudstone)

Clay mineral aggregate / Fine-grained siliciclastic sedimentary rock

Hardness: 2-3 on the Mohs scale. Color: Gray to dark grayish-green/black. Luster: Dull, earthy. Structure: Fine-grained, microcrystalline to cryptocrystalline, fissile (splits into thin layers). Cleavage: Perfect basal-like parting along bedding planes.

Hardness: 2-3 on the Mohs scale
Color: Gray to dark grayish-green/black
Luster: Dull, earthy

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the compaction and lithification of silt and mud/clay minerals in low-energy environments such as lakes, river deltas, floodplains, and deep ocean basins.

Uses & applications

Used in the manufacture of brick, tile, and Portland cement; source rock for petroleum and natural gas (including shale gas via fracking).

Geological facts

Shale is the most common sedimentary rock on Earth, accounting for over half of all sedimentary rocks in the crust. Many shales contain rich fossil beds due to the fine-grained sediment preserving soft details.

Field identification & locations

Identified by its fine grain size, soft nature (can usually be scratched with a penny or nail), and tendency to split easily into flat plates or thin slabs. Found abundantly in sedimentary basins worldwide.

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Banded Siltstone / Mudstone Pebble

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Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)

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Shale

Shale (clastic sedimentary rock)

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