mineral

Polished agate geode slice

Chalcedony (microcrystalline quartz, SiO₂), likely blue-gray agate with an open geode cavity

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; blue-gray translucent concentric banding, waxy to vitreous luster, and quartz lining or druzy crystals. Quartz has trigonal crystal structure and no cleavage; density is about 2.6 g/cm³.

Identified September 8, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited layers of chalcedony inside a volcanic vesicle, later leaving a cavity that may develop quartz crystals. Agates commonly formed in Cenozoic to older volcanic rocks over millions of years.

Uses & applications

Used for lapidary slabs, cabochons, carvings, ornaments, and jewelry; larger attractive slices are decorative collectibles.

Geological facts

The specimen appears cut and polished rather than raw, with its rough volcanic host rock retained around the edge. Blue coloration may be natural or enhanced by treatment, so laboratory testing is needed for certainty.

Field identification & locations

Identify by concentric curved banding, translucency, waxy polish, and a very hard surface that resists scratching by steel. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.