mineral
Banded agate
Chalcedony, microcrystalline SiO₂
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray, brown, and cream bands with a waxy-to-glassy luster. Microcrystalline quartz; no visible cleavage and conchoidal fracture. The specimen appears naturally broken or roughly shaped.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray, brown, and cream bands with a waxy-to-glassy luster. Microcrystalline quartz; no visible cleavage and conchoidal fracture. The specimen appears naturally broken or roughly shaped.
Formation & geological history
Forms as silica-rich fluids fill cavities and deposit successive layers in volcanic rocks; individual agate bands may form over long periods, commonly during the Cenozoic. Deposits occur worldwide, including Brazil, Uruguay, India, and the western United States.
Uses & applications
Used for beads, cabochons, carvings, ornaments, and small decorative objects; industrial chalcedony is sometimes used for hard-wearing components.
Geological facts
Agate’s curved or concentric bands reflect changing conditions as silica precipitated. A fresh broken surface can reveal patterns that are less obvious on the exterior.
Field identification & locations
Look for translucent silica with distinct, often curved bands and a glassy, shell-like fracture; it is much harder than glass. The photo shows a small banded fragment, but exact locality and identification are not certain from appearance alone.
