sedimentary

Shale

Shale (clastic sedimentary rock)

Hardness: 3 (Mohs scale), Color: Dark grey to brownish grey, Luster: Dull/Earthy, Structure: Fissile (splits into thin layers), Grain size: Fine-grained clay and silt.

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: Dark grey to brownish grey, Luster: Dull/Earthy, Structure: Fissile (splits into thin layers), Grain size: Fine-grained clay and silt.

Formation & geological history

Formed through the compaction of silt and clay-size mineral particles. These sediments are deposited in low-energy environments like lake bottoms, river deltas, and floodplains. Most shale is millions of years old, often dating to the Paleozoic or Mesozoic eras.

Uses & applications

Used as a raw material for brick, tile, and Portland cement. It is also source rock for oil and natural gas (shale gas).

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 often contains well-preserved fossils because of its fine grain size.

Field identification & locations

Identify it by its distinct 'sheet-like' layering and its ability to break along flat planes (fissility). It will not fizz with acid, unlike limestone. It is found in sedimentary basins worldwide.