sedimentary

Siltstone

Siltstone (primarily composed of quartz and clay minerals)

AI-generated identification · may be incorrect

Hardness: 3-4 on Mohs scale; Color: typically buff, grey, or tan; Luster: dull/earthy; Texture: fine-grained (gritty against teeth)

Hardness: 3-4 on Mohs scale
Color: typically buff, grey, or tan
Luster: dull/earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 3-4 on Mohs scale; Color: typically buff, grey, or tan; Luster: dull/earthy; Texture: fine-grained (gritty against teeth)

Formation & geological history

Formed by the lithification of silt-sized particles deposited in low-energy environments like river floodplains, lagoons, or deep water basins. Accumulation can occur over millions of years.

Uses & applications

Used as low-grade fill in construction, occasionally for flagstones or decorative landscaping if well-indurated.

Geological facts

Siltstone is often confused with shale, but it lacks the fissility (layering that splits easily) found in shale. It feels grittier than claystone but smoother than sandstone.

Field identification & locations

Identified by its fine grain and lack of visible crystals; the 'teeth test' (nibbling on a piece) reveals a gritty texture compared to smooth clay. Found globally in sedimentary basins.