sedimentary

Reddish Brown Claystone or Siltstone

Argillite / Siltstone / Claystone

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale), Color: Red-brown to chocolate brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None/Massive, Specific Gravity: 2.1-2.6

Identified May 7, 2026More sedimentary →

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Physical properties

Hardness: 2-3 (Mohs scale), Color: Red-brown to chocolate brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None/Massive, Specific Gravity: 2.1-2.6

Formation & geological history

Formed through the lithification of clay and silt particles deposited in low-energy environments like lake beds, river floodplains, or deep ocean basins. Often Fe-rich giving it the red-brown hue.

Uses & applications

Used largely in the brick and ceramic industry, as fill material in construction, and sometimes as a base for pigments. Fine-grained varieties are used in crafts.

Geological facts

This specimen appears water-worn or weathered into a smooth, rectangular shape. Claystones are the source of most fossils found in sedimentary layers.

Field identification & locations

Identify by its fine-grained texture (feels smooth/waxy), earthy smell when damp, and can often be scratched with a copper penny or steel knife. Found in sedimentary basins worldwide.