mineral

Polished agate geode

Chalcedony (microcrystalline quartz, SiO₂) with quartz druse crystals

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, vitreous to waxy luster, translucent gray-white banding, and a hollow cavity lined with sparkling quartz crystals; quartz has a trigonal crystal structure and no cleavage. The specimen appears polished and possibly enhanced, with minor iron-oxide brown coloration inside.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills gas cavities in volcanic rock, depositing concentric chalcedony bands and later quartz crystals. Formation commonly occurred in Cenozoic to older basaltic volcanic environments over thousands to millions of years.

Uses & applications

Used as a decorative specimen, paperweight, or jewelry and craft material; thin slices are used for cabochons and ornaments. It has little industrial value in this small polished form.

Geological facts

The outer bands are cryptocrystalline quartz, while the cavity contains larger euhedral quartz crystals. Agate’s vivid banding develops through repeated changes in groundwater chemistry and silica availability.

Field identification & locations

Identify it by concentric bands, waxy translucent chalcedony, a hollow drusy center, and hardness sufficient to scratch glass. Common sources include Brazil, Uruguay, Mexico, India, and the United States.