sedimentary / metamorphic

Rounded river cobble, likely quartz-rich sandstone or quartzite

Indeterminate; probable quartz arenite (sandstone) or low-grade quartzite, chiefly SiO₂

AI-generated identification · may be incorrect

Gray-brown, fine-grained, dull to slightly silky surface with rounded, water-worn shape and a prominent fracture. Likely hardness 6–7, massive texture, no visible cleavage, and moderate-to-high specific gravity (~2.6).

Identified September 3, 2026More sedimentary / metamorphic →

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Physical properties

Formation & geological history

Probably formed from compacted quartz-rich sand, possibly later metamorphosed into quartzite, then eroded and rounded in a river or shore environment; precise age cannot be determined from the image.

Uses & applications

Usually used as landscaping stone, paving, garden ornament, or a field specimen; quartzite may also serve as aggregate and durable building stone. Little jewelry value unless unusually patterned or polished.

Geological facts

The smooth outline indicates prolonged abrasion during transport, while the pale grains and resistance to weathering suggest abundant quartz. A fresh broken surface and acid test would help distinguish sandstone from quartzite.

Field identification & locations

Common in riverbeds, alluvial deposits, beaches, and glacial gravels worldwide. Look for visible sand grains and weaker cement in sandstone versus a hard, fused, sugary texture in quartzite; estimated value is $5–$30 unpolished, or $20–$100 as a decorative specimen.