sedimentary

River Pebble (Siltstone / Fine Sandstone)

Sedimentary Rock (siliciclastic clastic rock)

Hardness: 6-7 Mohs (quartz-rich); Color: Greyish-brown to dark slate grey; Luster: Dull, earthy; Texture: Fine-grained, smooth water-worn exterior with subtle sedimentary layering/banding; Specific Gravity: ~2.6-2.7

Hardness: 6-7 Mohs (quartz-rich)
Color: Greyish-brown to dark slate grey
Luster: Dull, earthy

Identified July 27, 2026More sedimentary →

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

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Physical properties

Formation & geological history

Formed by the deposition, compaction, and cementation of fine silts and quartz sands in fluvial or lakebed environments over millions of years. The rounded, smooth pebble shape is created by abrasion from water and sediment movement along riverbeds or shorelines.

Uses & applications

Commonly used as decorative garden pebbles, in river rock landscaping, aquariums, masonry work, or as worry stones for casual collectors.

Geological facts

Smooth river pebbles get their flattened oval or rounded shapes through a natural process called attrition, where rocks tumble over each other in fast-moving water, grinding away sharp edges over thousands of years.

Field identification & locations

Identified in the field by its smooth, water-worn rounded contours, fine-grained texture, matte surface, and faint concentric sediment layers. Commonly found in riverbeds, streams, glacial till, and coastal beaches worldwide.

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Sandstone or Siltstone

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