mineral

Polished agate geode

Chalcedony (microcrystalline quartz), SiO₂, with possible drusy quartz and iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-white and honey-brown banding, waxy to vitreous luster, irregular concentric layers, and a hollow cavity lined with tiny quartz crystals. Quartz has a trigonal crystal structure and indistinct cleavage, with conchoidal fracture; specific gravity about 2.60–2.65.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled gas cavities in volcanic rock, depositing chalcedony and later quartz in layers; commonly Cenozoic to older volcanic-hosted material. The specimen is cut and polished, exposing the cavity.

Uses & applications

Used as an ornamental slab, display specimen, cabochon, and occasionally in jewelry or carvings. It has modest value unless the banding, crystal lining, color, and polish are exceptional.

Geological facts

Agate forms from repeated pulses of silica-bearing fluids, producing distinctive rhythmic banding. The cavity is a small geode, and the golden color likely reflects iron oxides or included minerals.

Field identification & locations

Identify by curved concentric chalcedony bands, fine-grained texture, hardness, and quartz-like fracture; it should scratch glass but not be scratched by a steel blade. Common sources include Brazil, Uruguay, Mexico, India, and the western United States.