sedimentary

Gray River Pebble (Limestone or Greywacke)

Sedimentary Pebble (Calcite / Quartz composition)

Hardness: 3-7 on Mohs scale depending on exact composition; Color: Medium gray with subtle lighter veins and flecks; Luster: Matte to dull; Cleavage: None visible in smoothed pebble state; Texture: Smooth, water-worn exterior.

Hardness: 3-7 on Mohs scale depending on exact composition
Color: Medium gray with subtle lighter veins and flecks
Luster: Matte to dull

Identified July 27, 2026More sedimentary →

Explore Gray River Pebble (Limestone or Greywacke) in the encyclopedia →

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Physical properties

Formation & geological history

Formed from sedimentary rock layers, such as limestone or fine-grained sandstone, that were broken down and rounded over time through transport by river currents or ocean waves.

Uses & applications

Commonly used as decorative garden stone, landscaping aggregate, aquarium gravel, or aquascaping materials.

Geological facts

Water-worn river pebbles get their smooth, rounded shapes through mechanical weathering as they tumble along riverbeds against other stones and gravel over thousands of years.

Field identification & locations

Can be identified in the field by its rounded, smooth cobble or pebble shape and uniform gray coloration. Extremely common along river banks, lake shores, and beaches worldwide.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)

sedimentary

Shale

Shale (clastic sedimentary rock)

sedimentary