sedimentary

River Cobble (likely Quartzite or Sandstone)

Arenite or Meta-quartzite (SiO2)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Tan, brown, and grey with white patches; Luster: Dull/Earthy surface; Crystal structure: Microcrystalline to granular; Cleavage: None/Conchoidal fracture.

Hardness: 6-7 on Mohs scale
Color: Tan, brown, and grey with white patches
Luster: Dull/Earthy surface

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Tan, brown, and grey with white patches; Luster: Dull/Earthy surface; Crystal structure: Microcrystalline to granular; Cleavage: None/Conchoidal fracture.

Formation & geological history

Formed from the lithification of sand particles (sandstone) or the heat-and-pressure transformation of sandstone (quartzite). This specific specimen has been shaped and rounded by water erosion in a high-energy environment like a riverbed or shoreline.

Uses & applications

Used in landscaping, construction aggregate, and as a decorative garden stone; weathered cobbles are sometimes used for tool-making in prehistoric times.

Geological facts

This specimen shows 'impact marks' or 'chatter marks' which are small crescent-shaped fractures caused by rocks bumping into each other in turbulent water.

Field identification & locations

Identify in the field by its rounded shape and gritty or crystalline texture. Common in river valleys, glacial tills, and beaches. Collectors find these globally in most drainage basins.