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; waxy to glassy luster; reddish-brown, cream, and gray curved bands; cryptocrystalline, with no visible cleavage and conchoidal fracture. The rounded shape indicates tumbling or polishing.
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Physical properties
Hardness 6.5–7 Mohs; waxy to glassy luster; reddish-brown, cream, and gray curved bands; cryptocrystalline, with no visible cleavage and conchoidal fracture. The rounded shape indicates tumbling or polishing.
Formation & geological history
Forms when silica-rich groundwater deposits successive layers of chalcedony in cavities of volcanic rocks, commonly during the Cenozoic. Banding records changing chemistry and iron-oxide staining during repeated deposition.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and lapidary collections; durable polished agate is also used for small decorative objects.
Geological facts
Agate’s bands can be translucent and may show concentric, fortification-like patterns. Color enhancement and dyeing are common in commercial specimens.
Field identification & locations
Identify by fine curved banding, very high polish, hardness sufficient to scratch glass, and lack of cleavage; common sources include Brazil, Uruguay, Botswana, Mexico, and the United States. Exact locality cannot be confirmed from the image.
