gemstone

Carnelian agate (polished/chipped chalcedony)

Microcrystalline quartz, SiO₂; orange-red chalcedony colored mainly by iron oxides

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; translucent reddish orange to brown, waxy-to-glassy luster, cryptocrystalline quartz structure, and no visible cleavage. It appears partly polished or naturally water-worn, with botryoidal and irregular fracture surfaces.

Identified August 28, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing chalcedony in layers; iron produces the warm coloration. Individual agate formation commonly occurred during the Cenozoic or older volcanic episodes, depending on locality.

Uses & applications

Used for cabochons, beads, carvings, seals, and ornamental objects; durable aggregate-grade material has limited construction use.

Geological facts

Carnelian is the orange-red variety of chalcedony, while agate commonly shows banding or concentric deposition. Heating can intensify or redden its color.

Field identification & locations

Identify by its translucent warm color, waxy luster, hardness, conchoidal fracture, and lack of cleavage; it will scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, India, Madagascar, and the United States.