sedimentary

River Cobble (Quartzite-rich Sandstone)

Clastic Sedimentary Rock (Litharenite/Quartzite transition)

Hardness: 6-7 (Mohs scale); Color: Brown, tan, and grey with reddish iron staining; Luster: Dull/Earthy; Crystal Structure: Granular/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6-7 (Mohs scale)
Color: Brown, tan, and grey with reddish iron staining
Luster: Dull/Earthy

Identified April 22, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from the lithification of sand deposits, likely during the Paleozoic or Mesozoic eras. This specific specimen has been significantly weathered and smoothed by transport in a river or glacial environment, a process known as 'rounding'.

Uses & applications

Common river stones are used primarily in landscaping, decorative stone masonry, and construction aggregate. Extremely hard variants like quartzite are used as railway ballast.

Geological facts

The reddish-orange hues on the surface are 'desert varnish' or iron oxide staining, caused by long-term exposure to water and oxygen. The smooth, tear-drop shape suggests it traveled many miles in a high-energy water environment.

Field identification & locations

Identify in the field by its smooth, water-worn texture and 'pitting' from collisions in the stream bed. Commonly found in riverbeds, glacial tills, and alluvial fans. Collectors often look for these as 'base stones' for painting or as garden accents.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary