mineral

Polished blue banded agate cabochon/ornamental slab

Microcrystalline quartz (chalcedony), SiO₂, with blue coloring or inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent blue and gray-purple banding, waxy to vitreous luster, cryptocrystalline quartz with no visible cleavage. The straight-sided, glossy form appears cut and polished, possibly with surface coating or resin stabilization.

Identified August 11, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony over long periods, commonly during the Cenozoic or older volcanic episodes. Blue coloration may be natural but is often enhanced by dyeing.

Uses & applications

Used for ornamental objects, bookends, cabochons, jewelry, and lapidary display pieces; it is not generally used as a construction stone. Value is usually driven by pattern, color, workmanship, and size.

Geological facts

Agate banding records repeated changes in groundwater chemistry and silica deposition. Blue agate is frequently dyed because strongly saturated natural blue is uncommon.

Field identification & locations

Identify by curved or parallel translucent bands, waxy luster, very high polish, and inability to scratch with a steel knife; glass-like uniformity or dye concentrated in cracks suggests treatment. Common sources include Brazil, Uruguay, India, Madagascar, and Mexico.