gemstone

Polished carnelian agate

Microcrystalline quartz (chalcedony), SiO₂; iron-bearing carnelian/agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent orange-red to brown with cream banding or patches, vitreous-to-waxy luster, and no visible cleavage. It is a cryptocrystalline quartz aggregate with conchoidal fracture; the strong surface reflection indicates 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, depositing chalcedony and iron-oxide-colored layers, commonly during the Cenozoic or older volcanic episodes. Common sources include Brazil, Uruguay, India, Madagascar, Germany, and the United States.

Uses & applications

Used for beads, cabochons, carvings, seals, and ornamental objects; historically prized for signet rings. Commercial value is generally modest unless pattern, translucency, and color are exceptional.

Geological facts

Carnelian is the red-orange variety of chalcedony, while agate refers to patterned or banded chalcedony. Iron oxidation produces the characteristic warm colors, and heating can intensify them.

Field identification & locations

Identify by its waxy/glassy polish, translucency, orange-red color, and irregular chalcedony pattern; it should resist scratching by a steel blade. A gemological test is needed to distinguish natural color from dyed agate.