sedimentary

Shale

Shale (Lutite)

Hardness: 3 on Mohs scale; Color: Black, dark gray; Luster: Dull; Structure: Fissile (splits into thin layers); Cleavage: Perfect along bedding planes; Specific Gravity: 2.2 to 2.8.

Hardness: 3 on Mohs scale
Color: Black, dark gray
Luster: Dull

Identified May 10, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Black, dark gray; Luster: Dull; Structure: Fissile (splits into thin layers); Cleavage: Perfect along bedding planes; Specific Gravity: 2.2 to 2.8.

Formation & geological history

Formed from the compaction of silt and clay-size mineral particles. These particles are often deposited in low-energy environments like lake bottoms, river deltas, and floodplains over millions of years.

Uses & applications

Used primarily in the production of cement, bricks, and tiles. Dark shales are also a major source of natural gas and petroleum (shale oil) via hydraulic fracturing.

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 due to the fine-grained nature of the sediment.

Field identification & locations

Identify in the field by its thin, flat layers (fissility) and soft texture that can often be scratched with a fingernail or copper penny. It is commonly found in basins and ancient seafloors.