mineral

Tumbled banded agate (likely chalcedony)

Microcrystalline quartz, SiO₂; probable banded chalcedony/agate

AI-generated identification · may be incorrect

Small rounded, polished specimen with gray-green to black concentric or wavy banding and a waxy to vitreous luster. Hardness ~6.5–7 Mohs, no visible cleavage, cryptocrystalline quartz structure; specific gravity ~2.60.

Identified September 21, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater repeatedly fills cavities in volcanic rock, depositing successive chalcedony layers. The specimen’s exact geological age and locality cannot be determined from the photograph.

Uses & applications

Used for lapidary carvings, cabochons, beads, ornaments, and collectibles; common tumbled pieces generally have modest value.

Geological facts

The banding reflects changing chemistry, impurities, and growth conditions during cavity filling. Dark coloration may derive from iron, manganese, organic material, or enhancement/dyeing.

Field identification & locations

Identify by its very hard, fine-grained surface, curved bands, waxy luster, and inability to scratch with a steel knife; glass may be scratched by quartz, but field testing should be cautious. Banded agates occur worldwide, notably in Brazil, Uruguay, Mexico, India, Madagascar, and the United States.