sedimentary

Shale

Shale (Fissile Mudstone)

Hardness: 3 on Mohs scale; Color: Grey, black, or brown; Luster: Dull/Earthy; Structure: Fine-grained, clastic; Cleavage: High fissility (splits into thin layers)

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

Identified July 9, 2026More sedimentary →

Explore Shale in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 on Mohs scale; Color: Grey, black, or brown; Luster: Dull/Earthy; Structure: Fine-grained, clastic; Cleavage: High fissility (splits into thin layers)

Formation & geological history

Formed from the compaction of silt and clay-size mineral particles (mud) in low-energy environments like lake bottoms, river deltas, and floodplains over millions of years.

Uses & applications

Used in the production of bricks, tile, pottery, and Portland cement; also a source rock for oil and natural gas (shale gas).

Geological facts

Shale is the most common sedimentary rock on Earth, making up about 70 percent of the rocks in the Earth's crust. It often contains significant fossils due to its quiet deposition environment.

Field identification & locations

Identify by its ability to split into thin sheets (fissility) and its soft, clay-like smell when wet. Found globally in basins and mountainous regions where ancient seas once existed.