mineral
Banded agate (likely mossy/chalcedony-rich agate)
Microcrystalline quartz, SiO₂ (chalcedony); bands may include iron oxides and inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; translucent cream, gray, tan, and brown coloration with concentric or flowing banding. Waxy to vitreous luster, cryptocrystalline structure, no cleavage, and typical specific gravity near 2.60.
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Physical properties
Hardness about 6.5–7 Mohs; translucent cream, gray, tan, and brown coloration with concentric or flowing banding. Waxy to vitreous luster, cryptocrystalline structure, no cleavage, and typical specific gravity near 2.60.
Formation & geological history
Forms when silica-rich groundwater deposits successive layers of chalcedony in cavities and fractures, commonly in volcanic rocks; iron and other impurities create the brown bands and patches. Individual agates may range from Paleozoic to modern geologic ages.
Uses & applications
Used for cabochons, beads, carvings, bookends, and ornamental slabs; tougher material is also used for burnishing tools and laboratory mortars. This rough specimen has modest value unless cutting reveals exceptional patterning.
Geological facts
Agate is a variety of chalcedony distinguished by banding, and many patterns develop from rhythmic changes in fluid chemistry. Its fine texture allows a high polish.
Field identification & locations
Identify by its waxy surface, translucency, curved banding, and lack of visible large quartz crystals; a steel file should not easily scratch it. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.
