mineral

Small tumbled quartz pebble, possibly chalcedony

Quartz (SiO₂), likely microcrystalline chalcedony

AI-generated identification · may be incorrect

Small, rounded and translucent pale yellow-gray pebble with a vitreous-to-waxy luster. Quartz has Mohs hardness 7, trigonal crystal structure, no cleavage, and specific gravity about 2.65; the image does not show enough detail to confirm the variety.

Identified September 26, 2026More mineral →

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Physical properties

Formation & geological history

Quartz forms in many igneous, metamorphic, and sedimentary settings; chalcedony commonly precipitates from silica-rich fluids in cavities and fractures. Its age and whether it was naturally rounded or tumbled cannot be determined from the photo.

Uses & applications

Quartz is used in glass, electronics, abrasives, and jewelry; attractive chalcedony is cut or polished for ornaments and cabochons.

Geological facts

The specimen’s smooth shape and polish could result from tumbling, but natural water-worn pebbles can look similar.

Field identification & locations

Look for glassy luster, hardness sufficient to scratch glass, and absence of cleavage; these features help distinguish quartz from softer lookalikes. Quartz is widespread, including around Rio de Janeiro, but this photo cannot establish local provenance.