gemstone

Polished carnelian agate

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

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent orange, honey-brown, cream, and reddish zones with a vitreous-to-waxy luster. It has cryptocrystalline quartz structure, no visible cleavage, conchoidal fracture, and specific gravity near 2.6.

Identified September 15, 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 and iron-bearing bands; coloration develops through oxidation. Individual pieces may range from Paleozoic to Cenozoic in age, depending on the host deposit.

Uses & applications

Used for cabochons, beads, carvings, seals, and ornamental objects; polished pieces are inexpensive but attractive collector material.

Geological facts

Carnelian is the orange-red variety of chalcedony; agate refers to patterned or banded chalcedony. Heat treatment can intensify its red-orange color.

Field identification & locations

Identify it by translucency, waxy/glassy polish, lack of cleavage, and hardness sufficient to scratch glass; avoid confusing it with dyed glass or resin. Common sources include Brazil, Uruguay, India, Madagascar, and the United States.