mineral

Tumbled banded agate

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide and other inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; polished, waxy to vitreous luster; typically gray, brown, cream, and dark blue-black with irregular bands or brecciated patterns. Quartz has a trigonal crystal structure, but agate is cryptocrystalline and shows no visible cleavage.

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony and quartz over millions of years, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, ornaments, lapidary carvings, and decorative objects; small tumbled pieces are mainly collectible or ornamental.

Geological facts

Agate’s patterns result from changing fluid chemistry, impurities, and growth conditions. The dark areas may reflect iron/manganese oxides or included minerals; exact identification requires testing.

Field identification & locations

Common in volcanic terrains and alluvial gravels worldwide, including Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Identify by its waxy polish, very high scratch resistance, and translucent layered chalcedony; this specimen is likely dyed or naturally darkened in places.