gemstone

Polished banded agate (likely carnelian/brown agate)

Microcrystalline quartz, SiO₂ (chalcedony variety)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown, reddish-brown and cream banding with waxy-to-glassy luster. Quartz is trigonal, but the microcrystalline structure produces no visible cleavage; the piece is shaped and highly polished.

Identified September 5, 2026More gemstone →

Explore Polished banded agate (likely carnelian/brown agate) in the encyclopedia →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive chalcedony layers. Individual layers may span from millions to hundreds of millions of years in age, depending on the host formation.

Uses & applications

Used for cabochons, carvings, beads, ornaments, and small decorative objects; durable and attractive but generally modestly priced.

Geological facts

The flowing, parallel bands are characteristic of chalcedony; brown-red coloration commonly reflects iron oxides or hydroxides. Its elongated carved form may be a pendant, bead, or small ornamental carving.

Field identification & locations

Identify by testing hardness against ordinary steel or glass, observing waxy translucency and curved banding, and checking that it does not fizz in dilute acid. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.