sedimentary

Shale

Fissile mudstone (Shale)

Hardness: 3 on Mohs scale; Color: Grey, black, or brown; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: High fissility (splits into thin sheets); Specific Gravity: 2.4 - 2.8

Hardness: 3 on Mohs scale
Color: Grey, black, or brown
Luster: Dull/Earthy

Identified May 10, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, black, or brown; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: High fissility (splits into thin sheets); Specific Gravity: 2.4 - 2.8

Formation & geological history

Formed through the lithification of mud, silt, and clay particles deposited in low-energy environments like river deltas, lakes, or deep ocean floors over millions of years.

Uses & applications

Used as a source of natural gas (shale gas), as a component in the manufacture of Portland cement, and in the ceramic industry for making bricks and tiles.

Geological facts

Shale is the most common sedimentary rock on Earth, making up an estimated 70 percent of all sedimentary rock in the Earth's crust. It often contains well-preserved fossils.

Field identification & locations

Identify in the field by its tendency to break into thin, flat layers (fissility). It is commonly found in basins and ancient marine environments. Collectors look for shale layers that may contain leaf or insect fossils.