sedimentary

Shale

Shale (clay-sized silicate minerals)

Hardness: 3 on Mohs scale; Color: Gray to black; Luster: Dull/Earthy; Crystal structure: Non-crystalline/Microcrystalline clay minerals; Cleavage: Fissile (splits into thin sheets); Specific Gravity: 2.4 - 2.8

Hardness: 3 on Mohs scale
Color: Gray to black
Luster: Dull/Earthy

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the compaction of silt and clay-size mineral particles that we call mud. This occurs in low-energy environments like lake bottoms, river deltas, floodplains, and offshore from beach sands.

Uses & applications

Used as a source of clay for making bricks, tiles, and pottery. It is also an important source rock for oil and natural gas (shale gas) and is used in the manufacturing of cement.

Geological facts

Shale is the most common sedimentary rock on Earth. It often contains well-preserved fossils because of the fine-grained nature of the sediment. Black shales are rich in organic matter and are the primary source for many of the world's hydrocarbon deposits.

Field identification & locations

Identify in the field by its fine-grained texture and its tendency to break into thin, flat layers (fissility). It will not fizz with HCl unless it contains calcite. Often found in layered outcroppings near water sources or in valley floors.