sedimentary

Shale

Fissile Mudstone (primarily composed of clay minerals and quartz grains)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: typically grey, black, or reddish-brown; Luster: dull/earthy; Structure: fine-grained clastic texture; Cleavage: exhibits fissility (splits into thin, flat layers).

Hardness: 3 on Mohs scale
Color: typically grey, black, or reddish-brown
Luster: dull/earthy

Identified March 22, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically grey, black, or reddish-brown; Luster: dull/earthy; Structure: fine-grained clastic texture; Cleavage: exhibits fissility (splits into thin, flat layers).

Formation & geological history

Formed through the lithification of mud and silt particles, usually in low-energy environments like lake bottoms, river deltas, and deep ocean basins. The compaction occurs over millions of years under overlying pressure.

Uses & applications

Used as a major source of natural gas (shale gas) and oil. In construction, it is used for making bricks, tiles, and as a component in Portland cement.

Geological facts

Shale is the most common sedimentary rock on Earth. It serves as an excellent host for fossils because of the gentle deposition environment in which it forms. Famous deposits like the Burgess Shale contain some of the oldest well-preserved soft-bodied fossils.

Field identification & locations

Identify in the field by its tendency to break into thin sheets and its soft, muddy smell when wet. Commonly found in basins across the Appalachian Mountains, UK, and China. Collectors look for shale with visible plant or animal impressions.