sedimentary

Claystone / Mudstone

Mudstone (Hydrous aluminum silicate rich rock)

AI-generated identification · may be incorrect

Hardness: 1-2.5 Mohs. Color: Earthy brown to tan and reddish-brown. Luster: Dull, earthy. Structure: Fine-grained, non-cleavage, earthy fracture. Specific Gravity: 2.0-2.6.

Hardness: 1-2
Color: Earthy brown to tan and reddish-brown
Luster: Dull, earthy

Identified July 25, 2026More sedimentary →

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Physical properties

Hardness: 1-2.5 Mohs. Color: Earthy brown to tan and reddish-brown. Luster: Dull, earthy. Structure: Fine-grained, non-cleavage, earthy fracture. Specific Gravity: 2.0-2.6.

Formation & geological history

Formed by the compaction and lithification of fine-grained mud, clay, and silt particles deposited in calm water environments such as lakes, river floodplains, or shallow marine basins.

Uses & applications

Used in the manufacturing of bricks, ceramics, and cement, or as fill material in construction. Has limited value to collectors unless it contains fossils.

Geological facts

Mudstones make up over half of the sedimentary rocks in the Earth's crust. When subjected to higher heat and pressure over time, mudstone metamorphoses into slate.

Field identification & locations

Identify by its soft, earthy texture, fine-grained appearance, and tendency to feel smooth or sticky when moistened. Commonly found in riverbeds, lakeshores, and sedimentary basins worldwide.