mineral

Polished/tumbled agate or chert

Microcrystalline quartz (SiO₂), likely chalcedony with opaque impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown-gray, waxy to vitreous luster, fine cryptocrystalline structure, no visible cleavage, and conchoidal fracture. Subtle pale banding or flow-like markings suggest agate, though the image cannot confirm it.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing chalcedony and quartz in layers over long periods, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Commonly tumbled for collectors, cabochons, carvings, and decorative objects; agate is also used for beads and jewelry. Ordinary pieces typically have modest commercial value.

Geological facts

Agate is a variety of chalcedony distinguished by patterned bands, while visually similar jasper and chert may be more opaque and lack distinct banding.

Field identification & locations

Test for glass-like scratching with a steel knife cautiously—quartz should resist—and inspect edges for conchoidal fracture and translucent banding. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.