metamorphic

Water-worn quartzite or sandstone cobble

Quartzite (predominantly SiO₂), possibly quartz-rich sandstone

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs if quartzite (roughly 5–6 if sandstone); tan-gray, fine-grained, dull to slightly sugary luster, with no obvious cleavage. The elongated, rounded shape and smooth surface indicate prolonged abrasion by water or sediment transport.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely a weathered river, beach, or glacial cobble; quartzite formed when quartz-rich sandstone was metamorphosed under heat and pressure, commonly during older mountain-building events. Exact age and provenance cannot be determined from the photograph.

Uses & applications

Usually a natural curiosity, teaching specimen, or landscape stone; attractive pieces may be polished, but this specimen has little commercial or jewelry value.

Geological facts

Quartzite can resemble hard sandstone but typically fractures across grains rather than crumbling around them. A steel-file or glass-scratch test, performed inconspicuously, can help distinguish quartzite from softer sedimentary rock.

Field identification & locations

Look for a uniformly fused, gritty texture and resistance to scratching; quartz-rich cobbles commonly occur in streambeds, beaches, and glacial deposits worldwide. A hand lens and hardness test would improve identification.