mineral

Polished agate geode slice

Microcrystalline quartz (chalcedony), SiO₂, with possible druzy quartz

AI-generated identification · may be incorrect

Small cut and polished specimen showing concentric translucent chalcedony banding and a darker central cavity or inclusion. Quartz hardness is about 7 Mohs, vitreous to waxy luster, trigonal crystal structure; agate typically lacks visible cleavage and has specific gravity near 2.6.

Identified September 14, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and sometimes quartz crystals. The exact age cannot be determined visually; common sources include Cenozoic and older volcanic terrains.

Uses & applications

Used for cabochons, jewelry, ornaments, bookends, and mineral collections. Small polished slices are generally decorative rather than industrial.

Geological facts

The banded patterns arise from changing silica chemistry, impurities, and fluid conditions during cavity filling. The central dark area may be an iron-rich zone, another mineral, or a small vug.

Field identification & locations

Identify it by curved/concentric banding, translucent edges, waxy polish, and hardness sufficient to scratch ordinary glass. Common localities include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.