sedimentary

Siltstone

Siltstone (Detrital Sedimentary Rock)

Hardness: 3-4 (Mohs); Color: Gray to brownish-gray; Luster: Dull/Earthy; Texture: Fine-grained, gritty feel on teeth; Cleavage: None (conchoidal or irregular fracture)

Hardness: 3-4 (Mohs)
Color: Gray to brownish-gray
Luster: Dull/Earthy

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Gray to brownish-gray; Luster: Dull/Earthy; Texture: Fine-grained, gritty feel on teeth; Cleavage: None (conchoidal or irregular fracture)

Formation & geological history

Formed by the deposition and lithification of silt-sized particles (larger than clay but smaller than sand) in low-energy environments like river floodplains, lakes, or marine basins.

Uses & applications

Used primarily as fill material, in the manufacture of cement, and occasionally for interior floor tiles or as decorative garden stones.

Geological facts

Siltstone is often mistaken for shale, but it lacks the 'fissility' (tendency to split into thin sheets) that defines shale. It often contains micro-fossils.

Field identification & locations

Identify by its fine-grained texture that feels slightly abrasive compared to claystone. Common in sedimentary basins worldwide. Often found in riverbeds as rounded pebbles.