sedimentary
Agate Geode
Silicon Dioxide (Chalcedony/Quartz), SiO2
Hardness of 6.5 to 7 on the Mohs scale, concentric color banding ranging from gray, white, and black to translucent, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, concentric color banding ranging from gray, white, and black to translucent, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed in cavities within volcanic or sedimentary rocks through the deposition of silica-rich groundwater solutions over millions of years.
Uses & applications
Used widely in ornamental items, jewelry, carvings, and as a popular specimen for mineral collectors.
Geological facts
Geodes form when dissolved minerals slowly seep into a hollow cavity in a rock and crystallize along the walls inward over long periods.
Field identification & locations
Easily identified by its distinctive concentric banding and hollow or quartz-lined center. Found worldwide, notably in Brazil, Uruguay, and the United States.
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