sedimentary

Shale

Shale (clastic sedimentary rock)

Hardness: 3 (Mohs scale); Color: Grey, brown, or black; Luster: Dull/Earthy; Structure: Fissile, meaning it splits easily into thin layers; Specific Gravity: 2.4-2.8

Hardness: 3 (Mohs scale)
Color: Grey, brown, or black
Luster: Dull/Earthy

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Grey, brown, or black; Luster: Dull/Earthy; Structure: Fissile, meaning it splits easily into thin layers; Specific Gravity: 2.4-2.8

Formation & geological history

Formed from the compaction of silt and clay-sized mineral particles, commonly known as mud. This usually occurs in low-energy environments like lake bottoms, river deltas, or deep ocean floors over millions of years.

Uses & applications

Used in the production of bricks, tiles, and pottery. It is also an important source for natural gas and oil in the form of oil shale. Sometimes used as a component in cement.

Geological facts

Shale is the most common sedimentary rock on Earth, making up an estimated 70% of all sedimentary rock in the crust.

Field identification & locations

Identify by its thin, flat layers that break off easily (fissility). It is commonly found in areas that were formerly underwater or near ancient water basins. Collectors check for fossils, which are often preserved in shale beds.