mineral

Polished agate/geode fragment

Chalcedony (microcrystalline quartz, SiO₂) with quartz and probable iron/manganese oxides

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; waxy to vitreous luster, gray-brown coloration, and distinctive concentric banding with cavity-filling crystals. It has no obvious cleavage, conchoidal fracture, and specific gravity near 2.6.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive chalcedony and quartz bands in a volcanic gas cavity, commonly during the Cenozoic or older volcanic episodes. Trace oxides produced the dark brown and black patterns.

Uses & applications

Used as a lapidary stone, cabochon, ornamental object, and collector specimen; agate is also used for beads, carvings, and durable abrasives.

Geological facts

The specimen appears to be an agate nodule or geode slice retaining a rough outer rind and patterned interior. Banding reflects repeated changes in fluid chemistry during growth.

Field identification & locations

Identify it by its translucent chalcedony bands, curved/concentric patterns, quartz sparkle, and glassy conchoidal fracture; it will resist scratching by a steel knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.