sedimentary

River Stone / Siltstone

Siltstone (composed of lithified silt)

AI-generated identification · may be incorrect

Hardness: 3-5 on Mohs scale; Color: Grayish-green or tan; Luster: Dull/Earthy; Crystal Structure: Clastic (microscopic grains); Cleavage: None; Specific Gravity: ~2.6.

Hardness: 3-5 on Mohs scale
Color: Grayish-green or tan
Luster: Dull/Earthy

Identified April 1, 2026More sedimentary →

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Physical properties

Hardness: 3-5 on Mohs scale; Color: Grayish-green or tan; Luster: Dull/Earthy; Crystal Structure: Clastic (microscopic grains); Cleavage: None; Specific Gravity: ~2.6.

Formation & geological history

Formed from the accumulation and lithification of silt-sized particles (larger than clay but smaller than sand) in calm water environments like floodplains or lake beds. This specimen has been rounded by fluvial (river) erosion.

Uses & applications

Used in landscaping, decorative aquariums, and occasionally as a base material in construction. Polished versions are used for 'worry stones' or decorative crafts.

Geological facts

Siltstones are distinct from sandstones by their finer grain size and from shales by their lack of fissility (the ability to split into thin layers). Many river stones can be millions of years old, traveling miles from their original source.

Field identification & locations

Identify in the field by its smooth, river-worn texture and fine-grained matte surface. It should feel slightly gritty to the tongue or teeth unlike clay-based rocks. Commonly found in riverbeds, glacial deposits, and coastal areas.