mineral

Tumbled banded agate

Microcrystalline quartz (chalcedony), SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray, blue-gray, and brown concentric banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage, conchoidal fracture; specific gravity about 2.60.

Identified September 8, 2026More mineral →

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Physical properties

Hardness 6.5–7 Mohs; gray, blue-gray, and brown concentric banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage, conchoidal fracture; specific gravity about 2.60.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz. Individual agate layers may form over long geological intervals, commonly in Paleozoic–Cenozoic volcanic terrains.

Uses & applications

Used for jewelry, cabochons, carvings, ornaments, and lapidary specimens; common tumbled material has modest commercial value.

Geological facts

The curved internal bands reflect changing chemistry and flow conditions during cavity filling; some agates fluoresce weakly under UV light depending on trace impurities.

Field identification & locations

Identify by translucent edges, curved or fortification-like bands, waxy polish, and quartz hardness: it should resist scratching by a steel knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.