sedimentary

Siltstone

Siltstone (primarily SiO2 with Fe2O3)

Hardness: 6-7 Mohs; Color: Brown to reddish-brown; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: None/Irregular; Specific Gravity: 2.6-2.7

Hardness: 6-7 Mohs
Color: Brown to reddish-brown
Luster: Dull/Earthy

Identified June 8, 2026More sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Brown to reddish-brown; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Cleavage: None/Irregular; Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the lithification of silt-sized particles in low-energy depositional environments như river floodplains, lagoons, or deep-water basins. This specimen shows significant rounding, suggesting a fluvial (river) or coastal transport history.

Uses & applications

Used primarily as low-grade construction fill, garden landscaping, or occasionally for carving if the silt is sufficiently uniform.

Geological facts

Siltstone is distinct from shale because it lacks fissility (the ability to split into thin layers). It is more coarse than claystone but finer than sandstone.

Field identification & locations

Identify in the field by its gritty feel (less gritty than sandstone) and its inability to be scratched easily by a copper penny. Commonly found in riverbeds and sedimentary basins worldwide.