mineral

Polished agate geode slice

Chalcedony (microcrystalline quartz, SiO₂), banded agate variety

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, white, orange, and reddish-brown concentric banding; waxy to vitreous luster. Microcrystalline quartz has no visible cleavage, conchoidal fracture, and typically specific gravity near 2.6.

Identified August 14, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled cavities in volcanic rock, depositing chalcedony and iron-oxide bands over time; the host cavities are commonly Cenozoic to Mesozoic in age, depending on locality.

Uses & applications

Cut and polished for display, cabochons, jewelry, bookends, and ornamental objects. Common slices generally have modest collector value.

Geological facts

The layered patterns record repeated changes in fluid chemistry and oxidation conditions. The orange-red colors are commonly caused by iron oxides or hydroxides.

Field identification & locations

Identify it by curved, often translucent bands, a smooth polished surface, and quartz-like hardness; it should scratch ordinary glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.