mineral
Polished banded agate, likely moss or dendritic agate
Microcrystalline quartz (chalcedony), SiO₂, with iron/manganese inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; glossy vitreous luster; translucent cream upper zone with dark gray-brown chalcedony below and diffuse banding. Quartz has a trigonal crystal structure, but the specimen is cryptocrystalline and has no visible cleavage.
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Physical properties
Hardness about 6.5–7 Mohs; glossy vitreous luster; translucent cream upper zone with dark gray-brown chalcedony below and diffuse banding. Quartz has a trigonal crystal structure, but the specimen is cryptocrystalline and has no visible cleavage.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony in successive layers; commonly Cenozoic to older, depending on host rock.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and small polished collectibles; durable but generally inexpensive.
Geological facts
The contrasting zones result from changing fluid chemistry and trace-metal content during growth, while the dark area may contain iron or manganese oxides.
Field identification & locations
Identify by its waxy-to-glassy polish, hardness, curved chalcedony banding, and lack of cleavage; common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States. Exact variety cannot be confirmed without testing or an unpolished surface.
