sedimentary

Siltstone Pebble

Siltstone (fine-grained siliciclastic sedimentary rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Tan to light brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline visible grain; Cleavage: None; Specific Gravity: 2.3-2.6

Hardness: 6-7 (Mohs)
Color: Tan to light brown
Luster: Dull/Earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Color: Tan to light brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline visible grain; Cleavage: None; Specific Gravity: 2.3-2.6

Formation & geological history

Formed through the accumulation and lithification of silt-sized particles (larger than clay, smaller than sand) in low-energy aquatic environments like lake beds or floodplains. Most accessible specimens are from the Paleozoic to Cenozoic eras.

Uses & applications

Used primarily as fill material in construction, as a component of cement, or as decorative river rock in landscaping.

Geological facts

Siltstone is often mistaken for shale, but it lacks the 'fissility' (tendency to split into layers) that shale possesses. This specific specimen has been rounded by fluvial (water) erosion.

Field identification & locations

Identify in the field by its smooth feel compared to sandstone but grittier feel compared to claystone; it will not scratch easily with a fingernail. Commonly found in riverbeds and coastal areas.