sedimentary

Mixed River Pebbles

Polylithic rock fragments

Hardness varies from 3 to 7 depending on mineral content; colors include white, grey, brown, and green; luster ranges from dull to vitreous.

Identified November 3, 2026More sedimentary →

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Physical properties

Hardness varies from 3 to 7 depending on mineral content; colors include white, grey, brown, and green; luster ranges from dull to vitreous.

Formed through mechanical weathering, transportation by water, and deposition in riverbeds or marine environments over millions of years.

Used widely in landscaping, decorative ground cover, construction aggregates, and aquarium substrates.

River pebbles are smoothed and rounded by the abrasive action of water and sediment transport over long distances.

Identified by smooth, rounded edges and a mixture of mineral compositions; commonly found in riverbanks, dry washes, and beaches worldwide.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)