sedimentary

River Cobble (Quartzite or Sandstone)

Arenite or Meta-quartzite (SiO2 composition)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: Tan, beige, brown mottling; Luster: Dull/Earthy (unpolished); Structure: Granular/Clastic; Cleavage: None

Hardness: 6-7 (Mohs scale)
Color: Tan, beige, brown mottling
Luster: Dull/Earthy (unpolished)

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Tan, beige, brown mottling; Luster: Dull/Earthy (unpolished); Structure: Granular/Clastic; Cleavage: None

Formation & geological history

Formed through the accumulation of sand-sized grains in a high-energy environment like a riverbed or shoreline, eventually lithified and rounded by aquatic erosion over thousands of years.

Uses & applications

Commonly used in landscaping, as decorative garden stones, or in construction as aggregate. Smooth river stones are also popular for rock painting and decorative indoor displays.

Geological facts

The smooth, rounded shape is the result of 'saltation' and abrasion as the rock was tumbled along a riverbed by flowing water, wearing down all sharp edges.

Field identification & locations

Identify by its rounded, ovoid shape and granular texture. Found worldwide in active or ancient riverbeds, alluvial fans, and coastal regions. It will often scratch glass if it is quartz-heavy.