sedimentary

Siltstone

Siltstone (fine-grained clastic sedimentary rock)

AI-generated identification · may be incorrect

Hardness: 3-5 on Mohs scale; Color: Tan, brown, or grey; Luster: Dull/Earthly; Crystal Structure: Microcrystalline (clastic grains); Cleavage: None; Specific Gravity: 2.6-2.7.

Hardness: 3-5 on Mohs scale
Color: Tan, brown, or grey
Luster: Dull/Earthly

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 3-5 on Mohs scale; Color: Tan, brown, or grey; Luster: Dull/Earthly; Crystal Structure: Microcrystalline (clastic grains); Cleavage: None; Specific Gravity: 2.6-2.7.

Formation & geological history

Formed from the accumulation and lithification of silt-sized particles (larger than clay but smaller than sand) in low-energy environments like river floodplains, deltas, or lakes. Geological age varies by outcrop location.

Uses & applications

Primarily used as low-grade construction fill, occasional flagstone for landscaping, and for educational geological study.

Geological facts

Siltstone is often mistaken for shale, but it lacks the 'fissility' or the ability to split into thin, flat sheets. It feels slightly grittier against the teeth than claystone due to the silt content.

Field identification & locations

Identify in the field by its fine-grained texture that feels slightly abrasive (like very fine sandpaper) and its lack of visible layers compared to shale. Found globally in sedimentary basins.