mineral

Polished agate geode slice

Banded chalcedony (microcrystalline SiO₂), with druzy quartz and possible iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent white, gray, blue-gray, and pink banding with a dark crystalline cavity; waxy to vitreous luster and no cleavage. The specimen is cut and polished on one face, with a natural rough rind on the edge.

Identified August 18, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited concentric chalcedony bands inside a volcanic cavity, later leaving a quartz-lined vug; formation commonly occurred in Cenozoic volcanic rocks, though age depends on locality.

Uses & applications

Used as a decorative slab, display specimen, cabochon material, and lapidary stone; generally not suitable for structural construction.

Geological facts

Agate bands form incrementally as silica gels or fluids repeatedly enter a cavity. Dark areas may reflect manganese, iron, carbonaceous material, or included host rock rather than a distinct mineral.

Field identification & locations

Identify by curved concentric bands, translucent chalcedony, waxy polish, and quartz druze; common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States. Vinegar does not fizz, while quartz-like hardness resists scratching by steel.