Shale

Physical Properties

Hardness: 3 on Mohs scale; Color: Gray, black, or brown; Luster: Dull; Crystal structure: Non-crystalline visible particles; Cleavage: Fissile (splits into layers); Specific Gravity: 2.4-2.8

Formation & Geological History

Formed through the compaction and lithification of silt and clay-sized mineral particles, typically in calm water environments such as lake bottoms, floodplains, or deep oceans.

Uses & Applications

Used in the production of bricks, tiles, and pottery; a source of natural gas (shale gas) and oil; and crushed for use as sub-base material in road construction.

Geological Facts

Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the crust's sedimentary rocks. Fossil preservation is often excellent in fine-grained shales.

Field Identification & Locations

Identify by its fine-grained texture and its tendency to break into thin, flat plates (fissility). Commonly found in sedimentary basins worldwide. Rubbing it between teeth may feel smoother than sandier siltstones.

Identified on: 5/19/2026

Mode: Standard