sedimentary

River Pebble (Siltstone / Sandstone Pebble)

Sedimentary Rock (Quartz, Feldspar, Clay Minerals)

Hardness: 6-7 on Mohs scale (quartz-rich). Color: Brownish-tan to dark grey with reddish patches. Luster: Earthy, dull, and matte. Texture: Fine-grained, stream-rounded with micro-pitting. Cleavage: None. Specific gravity: 2.5 - 2.7.

Hardness: 6-7 on Mohs scale (quartz-rich)
Color: Brownish-tan to dark grey with reddish patches
Luster: Earthy, dull, and matte

Identified July 25, 2026More sedimentary →

Explore River Pebble (Siltstone / Sandstone Pebble) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the deposition, compaction, and cementation of fine mineral sand or silt grains in fluvial or lacustrine environments. Subsequently eroded, weathered, and rounded by stream or river transport over long periods.

Uses & applications

Commonly used as river rock landscaping material, aquarium substrate, construction aggregate, or simple tactile pocket stones.

Geological facts

Stream-rounded rocks get their smooth, egg-like shapes through a process called attrition, where water rolls rocks against one another, grinding down sharp edges and corners over thousands of years.

Field identification & locations

Identified by its well-rounded, smooth sub-oval shape, lack of visible large crystals, dull earthy appearance, and fine texture. Extremely common along riverbeds, lakeshores, gravel pits, and glacial till deposits worldwide.

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