mineral

Polished blue agate geode slice

Chalcedony (microcrystalline quartz), SiO₂, with possible quartz/drusy lining and iron-oxide coloration

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to vitreous luster, translucent blue-gray and tan concentric banding, and no obvious cleavage; the cavity is lined with tiny quartz crystals. Agate is cryptocrystalline and commonly has specific gravity around 2.6.

Identified August 25, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills gas cavities in volcanic lava, depositing chalcedony in successive bands and later quartz crystals in the hollow center. The specimen is likely Cenozoic or older volcanic-host material, though exact age cannot be determined from the image.

Uses & applications

Used as a decorative polished slice, cabochon, paperweight, and collector specimen; larger pieces are used for ornaments and jewelry. Value depends on color, banding, crystal lining, size, and polish.

Geological facts

The blue color may be natural trace-element coloration or enhanced by dyeing, a common treatment in commercial agate. Concentric bands record repeated changes in groundwater chemistry during cavity filling.

Field identification & locations

Identify by curved concentric bands, translucent chalcedony, a hard glassy surface, and an open quartz-lined cavity; it is commonly sourced from Brazil, Uruguay, Mexico, India, and the United States. Estimated value: $10–$40 for a small commercial slice, or $50–$150+ for especially vivid, well-crystallized material.