sedimentary

River Pebble (Siltstone / Fine-grained Sandstone)

Sedimentary Pebble (Siliclastic)

Hardness: 6-7 on the Mohs scale depending on quartz content. Color: Dark brown to reddish-brown. Luster: Matte to dull, smooth river-worn texture. Cleavage: None visible due to smooth erosion. Grain Size: Fine-grained.

Hardness: 6-7 on the Mohs scale depending on quartz content
Color: Dark brown to reddish-brown
Luster: Matte to dull, smooth river-worn texture

Identified July 26, 2026More sedimentary →

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

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Physical properties

Formation & geological history

Formed through the deposition, compaction, and cementation of fine mineral particles such as quartz, feldspar, and clay minerals. It acquired its rounded, smooth surface over long periods through hydraulic action and abrasion in riverbeds or coastal wave zones.

Uses & applications

Commonly used in landscaping, river rock decor, aquarium substrate, worry stones, and general rock polishing hobbies.

Geological facts

River pebbles undergo natural tumbling over hundreds or thousands of years. Smooth river stones were historically used as sling stones and primitive grinding tools.

Field identification & locations

Identified by its well-rounded, egg-like or flattened oval shape, matte dark surface, and fine-grained texture lacking visible crystals. Commonly found along riverbanks, gravel pits, and beaches worldwide.

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