sedimentary

Shale

Mudrock / Fissile Shale

Hardness 1-3 on Mohs scale, dark gray to black color, dull earthy luster, fine-grained microcrystalline texture, prominent fissile layering/cleavage, soft enough to scratch with a nail.

Identified July 25, 2026More sedimentary →

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Physical properties

Hardness 1-3 on Mohs scale, dark gray to black color, dull earthy luster, fine-grained microcrystalline texture, prominent fissile layering/cleavage, soft enough to scratch with a nail.

Formation & geological history

Formed from the compaction and lithification of silt and clay-size mineral particles in quiet, low-energy depositional environments such as deep marine basins, river deltas, lakes, and floodplains.

Uses & applications

Used primarily as a component in cement production, brick manufacturing, and as a raw material source for shale gas and oil extraction.

Geological facts

Shale is the most common sedimentary rock on Earth, accounting for roughly 50 to 70 percent of all sedimentary rocks in the crust. Dark shales often retain organic material that can turn into petroleum over geological time.

Field identification & locations

Identify in the field by its fine-grained texture, dark color, tendency to split into thin flat layers (fissility), and muddy smell when wet. Widely found in sedimentary basins worldwide.