sedimentary

Siltstone

Siltstone (primarily SiO2, Al2O3)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Gray, brown, or earthy; Luster: Dull/Matte; Structure: Clastic, fine-grained; Cleavage: None (conchoidal fracture possible)

Hardness: 6-7 on Mohs scale
Color: Gray, brown, or earthy
Luster: Dull/Matte

Identified May 3, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Gray, brown, or earthy; Luster: Dull/Matte; Structure: Clastic, fine-grained; Cleavage: None (conchoidal fracture possible)

Formation & geological history

Formed from the accumulation and lithification of silt-sized particles (clay and quartz) in low-energy environments like river floodplains, lakes, or deep marine basins.

Uses & applications

Commonly used in construction as fill material or road base; sometimes used for decorative landscaping or as paving stones if durable enough.

Geological facts

Siltstones are intermediate between sandstone and shale. They lack the fissility (layering that splits easily) of shale but have much finer grains than typical sandstone.

Field identification & locations

Identify by its gritty feel on the teeth (finer than sand but coarser than clay) and horizontal sedimentary laminations. Often found in riverbeds and coastal areas.