sedimentary

River Cobble (Quartzite / Sandstone)

Quartzite / Siliciclastic Sedimentary Rock

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale. Color: Grayish-tan to brownish-pink weathered exterior. Luster: Dull, earthy to sub-vitreous. Texture: Smooth, rounded, water-worn cobble.

Hardness: 6-7 on Mohs scale
Color: Grayish-tan to brownish-pink weathered exterior
Luster: Dull, earthy to sub-vitreous

Identified July 27, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Grayish-tan to brownish-pink weathered exterior. Luster: Dull, earthy to sub-vitreous. Texture: Smooth, rounded, water-worn cobble.

Formation & geological history

Formed through the accumulation and compaction of quartz-rich sand grains in riverine or beach environments, subsequently eroded and rounded by transport in stream beds or coastal waters.

Uses & applications

Commonly used in landscaping, river rock construction aggregate, decorative stone gardens, and general stone collecting.

Geological facts

Smooth cobbles like this are shaped over hundreds or thousands of years by the abrasive action of water and tumbling gravel in river channels.

Field identification & locations

Identified by its rounded cobble shape, smooth weathered surface, and high hardness (scratches steel). Found abundantly in riverbeds, glacial tills, and alluvial deposits worldwide.