sedimentary

River Cobble (likely Quartzite or Sandstone)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Gray, tan, or brownish; Luster: Dull to waxy; Texture: Fine-grained, rounded by water erosion; Cleavage: None (conchoidal fracture).

Hardness: 6-7 Mohs
Color: Gray, tan, or brownish
Luster: Dull to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Gray, tan, or brownish; Luster: Dull to waxy; Texture: Fine-grained, rounded by water erosion; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the deposition of sand-sized particles (sandstone) or the metamorphism of sandstone (quartzite). This specimen has been significantly rounded and smoothed by mechanical weathering in a high-energy river or stream environment over thousands of years.

Uses & applications

Common river stones are used primarily in landscaping, garden paths, decorative masonry, and as drainage aggregate. Extremely high-purity quartzite is used in glassmaking and metallurgy.

Geological facts

River stones like this one are time-capsules of geographical travel; their rounded shape indicates they have tumbled for miles from their original bedrock source. Quartzite is one of the most durable rocks on Earth's surface.

Field identification & locations

Identify by its rounded, smooth exterior and dull appearance when dry. It feels heavy for its size and cannot be scratched by a steel knife. Common in riverbeds, glacial moraines, and beaches worldwide.