mineral
Polished banded agate (likely Botswana or fortification agate)
Microcrystalline quartz, SiO₂, chiefly chalcedony with iron-oxide inclusions
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray-white, tan, and brown bands with a vitreous to waxy polish. Quartz is trigonal microscopically and has no cleavage; specific gravity is about 2.6.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray-white, tan, and brown bands with a vitreous to waxy polish. Quartz is trigonal microscopically and has no cleavage; specific gravity is about 2.6.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in successive layers; banding records changing fluids and impurities. Individual agate nodules commonly formed during the Cenozoic or older volcanic episodes.
Uses & applications
Used for cabochons, carvings, beads, bookends, and ornamental objects; it has modest jewelry and collector value.
Geological facts
The curved, concentric layering and translucency are characteristic of agate, while brown coloration commonly reflects iron oxides. The piece appears cut and polished, possibly shaped as a small carving or pendant.
Field identification & locations
Identify it by curved parallel bands, waxy translucency, glassy polish, and lack of obvious cleavage; a steel file should not easily scratch it. Common sources include Brazil, Uruguay, Botswana, Mexico, India, and the United States.
