sedimentary

Siltstone

Siltstone (composed of microscopic quartz and clay minerals)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs); Color: Tan, beige, or gray; Luster: Dull/Earthy; Crystal structure: Non-visible clastic grains; Cleavage: None; Specific gravity: 2.6

Hardness: 3-4 (Mohs)
Color: Tan, beige, or gray
Luster: Dull/Earthy

Identified July 3, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Tan, beige, or gray; Luster: Dull/Earthy; Crystal structure: Non-visible clastic grains; Cleavage: None; Specific gravity: 2.6

Formation & geological history

Formed by the deposition of silt-sized particles in low-energy environments like river floodplains, lagoons, or deep ocean basins. Often dates back to various geological periods where water-laid sediments accumulated.

Uses & applications

Used as a base material in construction, for fills, and occasionally as a low-quality building stone or paving material. Of interest to geologists for studying ancient environments.

Geological facts

Siltstone is intermediate between sandstone and shale. Unlike shale, it lacks the thin laminations or 'fissility' that causes the rock to split into thin sheets.

Field identification & locations

Identified by its fine-grained texture that feels gritty against the teeth but smoother than sandstone. It is commonly found in sedimentary basins worldwide. Focus on its lack of visible layers compared to shale.