sedimentary

Siltstone

Hardness: 3-4 on the Mohs scale; Color: Reddish-brown, gray, brown; Luster: Dull to earthy; Crystal structure: Microcrystalline, composed of silt-sized particles (0.002 to 0.06 mm); Cleavage: Poor or none, tends to break into blocky fragments; Specific Gravity: 2.5-2.7

Hardness: 3-4 on the Mohs scale
Color: Reddish-brown, gray, brown
Luster: Dull to earthy

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation, compaction, and cementation of fine-grained silt-sized mineral particles, mostly quartz and feldspar, typically in low-energy environments like river floodplains, deltas, lakes, or deep marine settings. Can range in geological age from Precambrian to recent.

Uses & applications

Used primarily in construction fill, road base materials, and occasionally as a decorative landscape stone or building stone.

Geological facts

Siltstone is intermediate in grain size and characteristics between shale and sandstone. When it splits easily along parallel layers, it is sometimes referred to as shaly siltstone.

Field identification & locations

Can be identified in the field by its fine-grained texture that feels gritty to the teeth (distinguishing it from smoother shale and coarser sandstone). Commonly found worldwide in sedimentary basins.