mineral

Polished blue-gray agate/geode slice (tentative)

Microcrystalline quartz (chalcedony), SiO₂, possibly with druzy quartz

AI-generated identification · may be incorrect

Smooth, polished, translucent blue-gray chalcedony with a darker cavity or vein lined by fine sparkling crystals. Quartz hardness is about 7 Mohs, vitreous to waxy luster, cryptocrystalline structure, and no distinct cleavage; the blue color may result from inclusions or treatment.

Identified August 20, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and sometimes quartz crystals in layers; formation commonly occurred during the Cenozoic or older volcanic episodes. The specimen appears cut, shaped, and polished.

Uses & applications

Used as a decorative stone, paperweight, cabochon, or jewelry component; attractive druzy examples are collectible. Common polished pieces typically sell for $10–$60, with larger or unusually vivid specimens reaching $100–$250.

Geological facts

Agate is a variety of chalcedony distinguished by banding, although this piece shows little obvious banding. The cavity’s glittering surface is consistent with druzy quartz.

Field identification & locations

Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Verify with a hardness test on an inconspicuous edge—quartz should scratch glass—while dyed or coated pieces may show concentrated color in cracks and uneven surfaces.