mineral

Banded agate (likely polished/tumbled)

Agate, a microcrystalline variety of quartz; SiO₂

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, vitreous to waxy luster, translucent gray-white and tan coloration, and fine curved concentric banding. It has no visible cleavage and consists of interlocking chalcedony/quartz fibers; specific gravity is about 2.60–2.65.

Identified August 22, 2026More mineral →

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Physical properties

Formation & geological history

Forms as silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony and quartz. Individual bands may form over long geological intervals, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative objects; its toughness and attractive banding make it popular in jewelry and collecting.

Geological facts

The specimen’s rounded shape and glossy surface indicate tumbling or polishing. The curved “fortification” bands are characteristic of agate rather than ordinary marble or glass.

Field identification & locations

Identify it by translucent edges, very fine natural banding, and inability to scratch it with a steel knife; quartz should scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.