gemstone

Polished carnelian agate

Microcrystalline quartz (chalcedony), SiO₂, colored mainly by iron oxides

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; translucent orange, cream, and reddish-brown banding or cloudy zones; vitreous to waxy luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth surface indicates tumbling or polishing.

Identified September 15, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock and later crystallizes as chalcedony; iron impurities produce the red-orange color. Individual pieces commonly formed in Cenozoic or older volcanic settings, depending on locality.

Uses & applications

Used for beads, cabochons, carvings, ornaments, and low-cost jewelry; attractive polished pieces are popular with collectors.

Geological facts

Carnelian is the orange-red variety of chalcedony, while agate typically shows banding or multicolored chalcedony zones. Heating can intensify its red color and may be used commercially.

Field identification & locations

Identify by its waxy translucence, orange-red coloration, quartz hardness, and lack of cleavage; it should scratch glass but not be scratched by a steel knife. Common sources include India, Brazil, Uruguay, Madagascar, and the United States.