mineral

Banded agate geode

Microcrystalline quartz (chalcedony), SiO₂, with quartz crystals

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, vitreous to waxy luster, translucent gray-white interior, and orange-brown to black concentric chalcedony bands. The cavity is lined with fine drusy quartz crystals; agate has no prominent cleavage and specific gravity near 2.6.

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater repeatedly filled a volcanic vesicle, depositing chalcedony bands and later quartz crystals. Most such agates formed in volcanic rocks during the Cenozoic or older, depending on locality.

Uses & applications

Used as lapidary slabs, decorative objects, jewelry, and mineral-collection specimens; attractive geodes can be polished or sliced.

Geological facts

The specimen appears to be a weathered, partially opened geode rather than a massive rock. Band colors commonly result from iron oxides and other trace impurities.

Field identification & locations

Identify by curved/concentric banding, waxy chalcedony, translucent edges, and a crystalline cavity; common sources include Brazil, Uruguay, Mexico, the United States, and Madagascar. Exact locality requires matrix and provenance information.