mineral
Polished blue-green agate slice
Agate, a banded microcrystalline variety of chalcedony (SiO₂), commonly colored by trace minerals
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent blue-green and white concentric banding, waxy to vitreous luster, cryptocrystalline quartz, no obvious cleavage, and specific gravity about 2.6. The center may contain drusy quartz or quartz-filled former cavity space.
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Physical properties
Hardness 6.5–7 Mohs; translucent blue-green and white concentric banding, waxy to vitreous luster, cryptocrystalline quartz, no obvious cleavage, and specific gravity about 2.6. The center may contain drusy quartz or quartz-filled former cavity space.
Formation & geological history
Forms when silica-rich groundwater fills gas cavities in volcanic rocks, depositing successive layers of chalcedony and quartz. Individual layers can form over long geological intervals, commonly in Cenozoic to older volcanic terrains.
Uses & applications
Used for cabochons, jewelry, ornamental slices, coasters, and lapidary displays. Commercial value depends mainly on color, banding, translucency, size, and polish.
Geological facts
Agate’s distinctive bands record changing chemistry and flow conditions during cavity filling; blue-green colors may be natural or enhanced by dyeing.
Field identification & locations
Identify it by curved concentric bands, translucent edges, very fine quartz texture, and hardness sufficient to scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.
