sedimentary

Shale

Lutaceous sedimentary rock

Hardness: 3-4 (Mohs scale); Color: gray, green, or buff; Luster: dull/earthy; Crystal Structure: microscopic clay minerals; Cleavage: fissile (splits into thin layers); Specific Gravity: 2.4-2.8

Hardness: 3-4 (Mohs scale)
Color: gray, green, or buff
Luster: dull/earthy

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: gray, green, or buff; Luster: dull/earthy; Crystal Structure: microscopic clay minerals; Cleavage: fissile (splits into thin layers); Specific Gravity: 2.4-2.8

Formation & geological history

Formed from the compaction of silt and clay-size mineral particles that we commonly call mud. This occurs in low-energy environments like lake beds or deep ocean basins over millions of years.

Uses & applications

Used as a source of clay for ceramics, cement manufacturing, and as a filler in paints and plastics. It is also a primary source of natural gas and oil in the energy sector (shale gas).

Geological facts

Shale is the most common sedimentary rock on Earth, accounting for about 70 percent of the rocks in the crust. It often contains well-preserved fossils because of the fine grain size.

Field identification & locations

Identify in the field by its very fine grain (cannot see individual grains with naked eye) and its tendency to break into thin, flat plates. Found worldwide in sedimentary basins.