mineral

Polished agate geode slice

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide coloration

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; waxy to vitreous luster, fine cryptocrystalline structure, no cleavage, and typically white-gray banding with orange-red and yellow hematite/goethite staining. The image appears to show a polished, cut slice with a small cavity or druzy area.

Identified August 9, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony over long periods, commonly during the Cenozoic or older volcanic episodes. Iron-bearing fluids create the red, orange, and yellow colors.

Uses & applications

Used for cabochons, bookends, ornaments, tabletops, and lapidary specimens; attractive slices have modest collector value.

Geological facts

Agate’s concentric or irregular bands record changing chemistry during cavity filling. A glassy polish, curved banding, and consistent hardness distinguish it from painted glass or resin.

Field identification & locations

Common sources include Brazil, Uruguay, Mexico, Madagascar, India, and the United States. Typical value is about $10–$40 for a small polished slice, or $50–$150+ for unusually vivid, well-patterned material.