gemstone

Polished banded agate (likely carnelian/chalcedony agate)

Microcrystalline quartz, SiO₂; primarily chalcedony with agate banding

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, brown, and bluish bands with waxy to glassy luster. Cryptocrystalline quartz has no visible cleavage, uneven fracture, and typically specific gravity near 2.60.

Identified September 17, 2026More gemstone →

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

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Physical properties

Formation & geological history

Forms as silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz; banding may develop over long geological intervals, commonly in Cenozoic to older volcanic terrains.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary specimens; durable but generally modestly priced unless banding or color is exceptional.

Geological facts

Agate’s distinctive curved or concentric banding records changing chemistry and fluid conditions during cavity filling. The surface appears polished or naturally water-worn.

Field identification & locations

Identify by curved translucent bands, waxy luster, and hardness sufficient to scratch glass; common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. A gemological test can distinguish dyed material from natural color.