gemstone

Polished orbicular agate (likely Botswana agate)

Microcrystalline quartz, SiO₂, chiefly chalcedony with iron-oxide inclusions

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; waxy to vitreous luster; gray, cream, brown, and black concentric or orbicular banding; cryptocrystalline quartz with no visible cleavage, conchoidal fracture, and typical specific gravity near 2.6. The rounded, glossy surface is human-polished.

Identified September 8, 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; iron and manganese create the darker patterns. Comparable agates are mainly Cenozoic to Mesozoic, though exact age requires locality data.

Uses & applications

Used for cabochons, beads, carvings, worry stones, and ornamental objects; durable and attractive but generally modestly priced.

Geological facts

Orbicular patterns are produced by rhythmic mineral deposition, sometimes around tiny nuclei or inclusions. “Botswana agate” is a trade name for strongly banded agate from Botswana and nearby southern African sources.

Field identification & locations

Identify by hardness, glassy/waxy polish, translucent edges, conchoidal fracture, and curved banding; it should not scratch easily with a steel knife. Common sources include Botswana, Brazil, Uruguay, Mexico, India, and the United States.