sedimentary

Rounded quartz-rich cobble

Likely quartzite or quartz-rich sandstone; exact identification requires a hardness and acid test

AI-generated identification · may be incorrect

Pale gray, fine-grained, dull to subtly sparkling, with no visible cleavage and a smoothly water-worn surface. Quartz-rich material typically has Mohs hardness 6.5–7 and specific gravity about 2.6; quartzite is harder and more resistant than sandstone.

Identified September 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Probably a glacial or stream-rounded cobble derived from metamorphosed sandstone (quartzite) or compact quartz sandstone. Its precise geologic age and source cannot be determined from the photograph.

Uses & applications

Usually collected as a decorative or landscaping stone; quartzite may be crushed for aggregate, roadstone, and construction. It has little jewelry value unless unusually pure, patterned, or attractive.

Geological facts

The rounded shape reflects prolonged abrasion during transport by water, ice, or surf. A glass-scratching test supports quartz content, while dilute hydrochloric acid should produce little or no reaction.

Field identification & locations

Common in river gravels, beaches, glacial deposits, and mountain regions. Quartzite shows fused quartz grains and breaks across grains; sandstone more often feels granular and may crumble or show visible cement.