metamorphic

Rounded gray cobble, likely quartzite or fine-grained sandstone

Quartzite (SiO₂), provisional identification

AI-generated identification · may be incorrect

Light gray, smooth and strongly weathered/rounded, with a fine granular texture and dull to slightly silky luster; quartzite has Mohs hardness about 7, no cleavage, and specific gravity around 2.65. The image cannot reliably distinguish quartzite from durable sandstone or graywacke.

Identified August 19, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely a glacially or fluvially transported cobble shaped by abrasion; quartzite forms when quartz-rich sandstone is metamorphosed under heat and pressure, commonly during mountain-building. Its precise geological age and source cannot be determined visually.

Uses & applications

Common quartzite is used as aggregate, roadstone, landscaping rock, and building stone; attractive pieces may be polished or collected but are generally low-value.

Geological facts

Quartzite resists weathering more strongly than most surrounding rocks, so it commonly remains as rounded stream or glacial cobbles. A steel file should not scratch true quartzite; sandstone may show more obvious grains and weaker resistance.

Field identification & locations

Common in streambeds, glacial deposits, beaches, and upland gravels worldwide; inspect a fresh chip for interlocking quartz grains and test with a steel nail/file. Estimated value: $1–$10 as a landscape or field specimen, potentially $10–$30 if unusually attractive and polished.