mineral
Banded Agate (Tumbled)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness 6.5-7 on Mohs scale; color ranges from grey, translucent white, and brownish tones with characteristic concentric banding; vitreous to waxy luster; trigonal crystal system (microscopic); no cleavage; specific gravity ~2.6.
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Physical properties
Hardness 6.5-7 on Mohs scale; color ranges from grey, translucent white, and brownish tones with characteristic concentric banding; vitreous to waxy luster; trigonal crystal system (microscopic); no cleavage; specific gravity ~2.6.
Formation & geological history
Formed by the deposition of silica solutions within gas vesicles (cavities) in volcanic rocks or near-surface sedimentary environments over long geological time periods.
Uses & applications
Popular for lapidary work, jewelry making, decorative tumbling, cabochons, and crystal collecting.
Geological facts
Agate is named after the Achates River (now the Dirillo) in Sicily, where it was discovered in ancient times. Its distinct banding is caused by alternating layers of chalcedony and quartz.
Field identification & locations
Identified by its distinctive translucency, fine microcrystalline texture, and parallel or concentric banding. Commonly found in Brazil, Uruguay, Madagascar, the US (Lake Superior region), and India. Small tumbled specimens like this are ideal for beginner collectors.
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