mineral
Banded agate (likely botryoidal chalcedony)
Agate, microcrystalline quartz (SiO₂), commonly chalcedony with quartz bands
AI-generated identification · may be incorrectHardness 6.5–7; gray, white, and brown concentric banding; waxy to vitreous luster; cryptocrystalline, with no visible cleavage and conchoidal fracture. The rounded, layered form may be botryoidal chalcedony.
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Physical properties
Hardness 6.5–7; gray, white, and brown concentric banding; waxy to vitreous luster; cryptocrystalline, with no visible cleavage and conchoidal fracture. The rounded, layered form may be botryoidal chalcedony.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers over time; commonly Cenozoic to older volcanic-host-rock occurrences.
Uses & applications
Used for cabochons, carvings, beads, bookends, and small collector specimens; attractive banding gives it modest lapidary value.
Geological facts
Agate bands record changing chemistry and fluid conditions during cavity filling. Exact locality and treatment cannot be determined from the photograph alone.
Field identification & locations
Identify by its waxy surface, very fine concentric bands, lack of cleavage, and ability to scratch ordinary glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.
