Shale

Physical Properties

Hardness: 3 on Mohs scale; Color: Black, grey, or dark brown; Luster: Dull or earthy; Structure: Clastic, fine-grained; Cleavage: Exhibits fissility (splits into thin layers); Specific Gravity: 2.4 - 2.8.

Formation & Geological History

Formed through the compaction of silt and clay-size mineral particles (mud). It typically forms in low-energy environments such as lakes, river deltas, and floodplains. Age varies from Precambrian to Cenozoic.

Uses & Applications

Used in the production of cement, bricks, and tile. It is also a primary source rock for natural gas and petroleum (shale gas).

Geological Facts

Shale is the most common sedimentary rock on Earth, accounting for about 70 percent of the rocks in the crust. Some black shales are rich in organic matter and contain fossils.

Field Identification & Locations

Identify by its fine-grained texture and its tendency to break along flat, thin planes (fissility). It will not fizz with HCl unless it contains calcite. Commonly found in sedimentary basins worldwide.

Identified on: 4/18/2026

Mode: Standard