sedimentary

River Pebble

Polymictic rock fragment

Hardness varies by mineral content, typically Mohs 6-7. Color ranges from grey to brown with a smooth, water-worn luster.

Identified October 29, 2026More sedimentary →

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Physical properties

Hardness varies by mineral content, typically Mohs 6-7. Color ranges from grey to brown with a smooth, water-worn luster.

Formed through the continuous water transport, abrasion, and weathering of larger parent rocks in riverbeds over thousands of years.

Used in landscaping, decorative garden pathways, construction aggregates, and as a tactile object for collection.

River pebbles are smoothed by the natural tumbling action of water and sediment, a process that can take many years to achieve.

Identified by its smooth, rounded shape and polished surface found along riverbanks and ancient stream beds.

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)