sedimentary

Siltstone or Fine-grained Sandstone pebble

Siltstone (primarily SiO2 with clay minerals)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Tan to dull brownish-green; Luster: Dull/Earthy; Crystal structure: Clastic (non-visible crystals); Cleavage: None; Specific gravity: 2.3-2.6

Hardness: 6-7 (Mohs)
Color: Tan to dull brownish-green
Luster: Dull/Earthy

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Color: Tan to dull brownish-green; Luster: Dull/Earthy; Crystal structure: Clastic (non-visible crystals); Cleavage: None; Specific gravity: 2.3-2.6

Formation & geological history

Formed via the accumulation and lithification of silt-sized particles (smaller than sand, larger than clay) in low-energy environments like river deltas, floodplains, or lake beds. These typically date from many geological eras depending on location.

Uses & applications

Largely used as fill material in construction or as river rock for landscaping. Generally lacks industrial or gemstone value unless it possesses unique banding or fossil inclusions.

Geological facts

Siltstones are often differentiated from shales by their lack of fissility (the ability to split into thin layers). Over millions of years, heat and pressure can transform these into metamorphic rocks like slate or phyllite.

Field identification & locations

Identify in the field by its gritty texture (finer than sandpaper but rougher than clay) and dull appearance. It is commonly found in riverbanks, glacial tills, and coastal areas. This specific specimen appears to be a water-worn, rounded river pebble.