gemstone

Polished blue chalcedony (likely blue agate)

Cryptocrystalline quartz, SiO₂; chalcedony variety

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; pale blue-white, translucent, waxy to vitreous luster, no visible cleavage, and very fine fibrous/microcrystalline quartz structure. The spherical, glossy surface indicates extensive polishing; dye treatment is possible but not evident.

Identified August 19, 2026More gemstone →

Explore Polished blue chalcedony (likely blue agate) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, commonly during the Cenozoic and older volcanic episodes. Layering or banding may be hidden by the uniform blue coloration and rounded cut.

Uses & applications

Used for cabochons, beads, carvings, spheres, and decorative objects; durable enough for jewelry and ornamental stone. Common commercial pieces have modest value.

Geological facts

Chalcedony is a quartz aggregate rather than a single large crystal, so it lacks quartz’s crystal faces and cleavage. Blue coloration can result from trace minerals, microscopic inclusions, or dyeing.

Field identification & locations

Commonly found in volcanic terrains, especially Brazil, Uruguay, India, Madagascar, and the western United States. Confirm with a hardness test on an inconspicuous area: it should scratch glass; uniform color and color concentration in cracks suggest dye.