Shale

Physical Properties

Hardness: 3 on Mohs scale; Color: Grey, black, or dark brown; Luster: Dull/Earthy; Crystal Structure: Microcrystalline (clay minerals); Cleavage: Fissile (splits into thin layers); Specific Gravity: 2.4 - 2.8.

Formation & Geological History

Formed through the lithification of mud and silt particles in low-energy environments like river deltas, lakes, or deep ocean floors. Often dates from the Paleozoic to Mesozoic eras.

Uses & Applications

Used in the production of bricks, cement, and pottery. It is also a primary source rock for oil and natural gas (shale gas) and is used in construction as fill material.

Geological Facts

Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the sedimentary rocks in the Earth's crust. It is a frequent host for well-preserved fossils due to the fine grain size.

Field Identification & Locations

Identify by its ability to split into thin flat sheets (fissility). In the field, look for 'platy' or flaking layers in riverbeds or roadcuts. It will often feel smooth to the touch unlike sandstone.

Identified on: 4/22/2026

Mode: Standard