gemstone

Polished banded agate (likely blue-green chalcedony)

Microcrystalline quartz, SiO₂; cryptocrystalline chalcedony with agate banding

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent blue-green and white concentric bands, waxy-to-glassy luster, cryptocrystalline structure, no visible cleavage, specific gravity about 2.6. The rounded form appears polished or tumbled, possibly with dye or surface coating.

Identified August 20, 2026More gemstone →

Explore Polished banded agate (likely blue-green chalcedony) 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 layers of chalcedony over long periods, commonly during the Cenozoic or older volcanic episodes. Exact locality and age cannot be determined from the image.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and small display specimens; agate is also used for durable decorative objects and historically for precision mortars. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.

Geological facts

Concentric banding records changing chemistry and silica deposition within a former gas vesicle. Blue-green coloration may be natural but is often enhanced by dyeing.

Field identification & locations

Identify by its translucent waxy appearance, curved banding, quartz-like hardness, and resistance to scratching by steel; glassy bubbles or perfectly uniform color would suggest glass instead. Collector value is usually modest unless the pattern, color, transparency, and provenance are exceptional.