gemstone

Polished banded agate

Agate, microcrystalline quartz (SiO₂), commonly chalcedony with quartz bands

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; waxy to vitreous luster; cream, honey, and brown concentric banding; cryptocrystalline quartz with no visible cleavage; specific gravity about 2.6. The smooth oval surface indicates a cut and polished specimen.

Identified August 13, 2026More gemstone →

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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. Individual bands may form over long intervals, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, carvings, bookends, and ornamental objects; durable and popular in inexpensive jewelry and collections.

Geological facts

Agate banding can reveal changing chemistry, temperature, and fluid flow during cavity filling. The specimen may be dyed, though its warm cream-and-brown colors can also be natural.

Field identification & locations

Identify by its translucent-to-opaque fine banding, quartz hardness, and lack of cleavage; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.