sedimentary

Rounded river cobble

Likely quartz-rich sandstone or metamorphosed quartzite; exact identification is uncertain from the photograph

AI-generated identification · may be incorrect

Gray, smoothly water-worn, fine-grained and dull to slightly satin-lustrous, with rusty iron-oxide staining. Likely hardness about 6–7 Mohs if quartz-rich; cleavage absent and specific gravity approximately 2.6.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from compacted quartz-rich sediment, or from sandstone recrystallized into quartzite, then rounded by prolonged stream or beach abrasion. Its precise geological age and formation locality cannot be determined visually.

Uses & applications

Suitable as a decorative stone, garden stone, paperweight, or landscaping material; it has little jewelry value unless cut and polished.

Geological facts

The elongated shape and uniformly rounded edges indicate transport by moving water or waves. Pale streaks and orange-brown patches may reflect quartz-rich grains and weathered iron minerals.

Field identification & locations

Common in riverbeds, beaches, glacial deposits, and gravel bars. Test with a steel nail and glass, inspect a fresh fracture for interlocking quartz grains, and use dilute hydrochloric acid to check for carbonate cement; no fizz suggests a silicate rock.