sedimentary

Shale

Shale (Sedimentary rock composed of mud/clay minerals)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Black, dark gray, or charcoal; Luster: Dull or earthy; Crystal structure: Microcrystalline/clastic; Cleavage: Fissile (breaks into thin layers); Specific gravity: 2.4 - 2.8

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

Identified May 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the compaction and lithification of silt and clay-sized mineral particles, typically in low-energy environments like lake beds or deep ocean basins. Ages range from Precambrian to Cenozoic.

Uses & applications

Used in the production of bricks, tile, and Portland cement. It is also an important source of natural gas and oil when it contains organic matter (oil shale).

Geological facts

Shale is the most common sedimentary rock on Earth. It often contains well-preserved fossils because the fine-grained sediment protects small organisms from decay.

Field identification & locations

Identify in the field by its tendency to split into thin, flat sheets (fissility). It feels smooth but slightly gritty and will not fizz with acid unless it contains calcite.