mineral

Blue agate slice with quartz crystal cavity

Chalcedony (microcrystalline SiO₂) with quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; deep blue, white-banded edge, vitreous to waxy luster, cryptocrystalline chalcedony, with sparkling drusy quartz lining a cavity. The vivid blue color is commonly enhanced by dyeing.

Identified September 12, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills gas vesicles or cavities in volcanic rock, depositing chalcedony and later quartz crystals. Agates generally formed during the Cenozoic or older volcanic episodes, depending on locality.

Uses & applications

Used as a polished decorative specimen, pendant, paperweight, or jewelry component; blue material is often dyed to improve color. Small slices have modest decorative and collector value.

Geological facts

The rough outer edge preserves the original geode wall, while the hollow center is a quartz-lined vug. Natural blue agate is uncommon, so intensely uniform blue specimens are typically treated.

Field identification & locations

Identify by concentric chalcedony banding, a hard glassy surface, and quartz sparkle; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, and India.