mineral
Tumbled banded agate
Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide and other trace-coloring inclusions
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; gray, cream, tan, and brown curved banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smoothly polished, rounded surface indicates a tumbled specimen.
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Physical properties
Hardness 6.5–7 Mohs; gray, cream, tan, and brown curved banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smoothly polished, rounded surface indicates a tumbled specimen.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony over long periods, commonly during the Cenozoic or older volcanic episodes. The pictured piece may be Botswana agate or another banded agate, but locality cannot be confirmed visually.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and inexpensive jewelry; also collected for its attractive natural banding.
Geological facts
Agate is a variety of chalcedony, and its bands can record changing chemistry, temperature, and fluid flow during cavity filling.
Field identification & locations
Identify by its fine curved or concentric bands, translucent edges, waxy polish, and quartz-like hardness; it should resist scratching by steel. Common sources include Brazil, Uruguay, Botswana, Mexico, India, and the United States.
