sedimentary

Mudstone

Argillite / Siliciclastic sedimentary rock

AI-generated identification · may be incorrect

Hardness: 2-4 (Mohs); Color: Gray, brown, black, with green moss/algae growth; Luster: Dull or earthy; Structure: Fine-grained, no visible crystals or bedding; Specific Gravity: 2.2-2.8

Hardness: 2-4 (Mohs)
Color: Gray, brown, black, with green moss/algae growth
Luster: Dull or earthy

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 2-4 (Mohs); Color: Gray, brown, black, with green moss/algae growth; Luster: Dull or earthy; Structure: Fine-grained, no visible crystals or bedding; Specific Gravity: 2.2-2.8

Formation & geological history

Formed from the lithification of mud and clay particles deposited in low-energy environments like lake beds, floodplains, or deep marine basins over millions of years.

Uses & applications

Primarily used as fill material in construction or as a source material for brick making and ceramics. Rarely used for decorative purposes unless metamorphosed.

Geological facts

Mudstone is the most common sedimentary rock on Earth, making up about 65% of all sedimentary rocks found in the crust.

Field identification & locations

Identify by its smooth, fine-grained texture that does not scratch glass and its tendency to break into blocky fragments rather than thin sheets (unlike shale). Common in riverbeds and eroded hillsides.