sedimentary

Shale

Fissile mudrock (composed of clay-sized particles and detrital grains)

Hardness: 3 on Mohs scale; Color: typically grey, black, or tan; Luster: dull/earthy; Crystal structure: non-crystalline (clastic); Cleavage: exhibits fissility (splits into thin layers); Specific gravity: 2.4 - 2.8

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

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of mud and clay particles deposited in slow-moving water (lakes, river deltas, or floodplains). It represents millions of years of sediment accumulation and compaction.

Uses & applications

Used as a raw material for brick, tile, and pottery manufacturing. When crushed, it is used in road base construction. It is also a significant source of natural gas and oil via hydraulic fracturing.

Geological facts

Shale is the most common sedimentary rock on Earth, making up about 70 percent of all sedimentary rocks in the Earth's crust. It is often the host rock for fossils due to the low-energy environment in which it forms.

Field identification & locations

Identify in the field by its thin, flat layers that break easily along parallel planes (fissility). It will often have a smooth, soapy feel if rich in clay. Common in basins and areas with historical deltaic activity.

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Sandstone (Quartz-rich)

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Sandstone (with man-made markings)

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