mineral

Polished agate geode slice

Microcrystalline quartz (chalcedony), SiO₂, with possible quartz-lined or calcite-filled cavity

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown, gray, translucent chalcedony surrounds an opaque white center. Waxy to glassy luster, cryptocrystalline structure, no visible cleavage, and conchoidal fracture; the white filling may be quartz, calcite, or another mineral.

Identified September 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled a cavity in volcanic rock, depositing chalcedony in layers and later filling the interior. Agates commonly formed during the Cenozoic and Mesozoic eras, depending on locality.

Uses & applications

Used as decorative slices, cabochons, bookends, and collectible specimens; attractive pieces may be set in jewelry or used for lapidary crafts.

Geological facts

The concentric or irregular banding records successive pulses of mineral-rich fluid. The specimen appears cut and polished, with a natural cavity or contrasting mineral center.

Field identification & locations

Identify by its fine banding, waxy chalcedony, translucent margins, and very hard surface that resists scratching by steel. Common sources include Brazil, Uruguay, Mexico, India, and the United States.