mineral

Polished agate/geode slice

Chalcedony (microcrystalline quartz, SiO₂), likely agate with an altered druzy/quartz interior

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; pale gray translucent-to-opaque center with a cream, pink, and reddish-brown banded rim; waxy to slightly vitreous luster. Agate has cryptocrystalline quartz and commonly shows concentric banding, with no obvious cleavage; density about 2.6 g/cm³.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled a cavity in volcanic rock, depositing chalcedony and quartz in successive layers. The exact age is uncertain; agates commonly form in volcanic cavities from Paleozoic to Cenozoic settings.

Uses & applications

Used as ornamental slices, cabochons, bookends, and jewelry; attractive specimens typically sell for about $5–$30, while larger or strongly patterned examples may reach $50–$150.

Geological facts

The irregular pink-red margin and gray interior strongly suggest an agate slice or partially filled geode, possibly heat-treated or polished. The image does not show enough diagnostic detail for a precise locality or treatment determination.

Field identification & locations

Identify by its fine banding, waxy chalcedony, curved cavity outline, and lack of large visible crystals. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and volcanic regions of Europe; the Rhône-area location is geologically plausible for chalcedony-bearing volcanic or hydrothermal material, though not diagnostic.