sedimentary
Agate Geode
Silicon Dioxide (SiO2) - Chalcedony variety
Hardness of 6.5 to 7 on the Mohs scale, earthy to vitreous luster, cryptocrystalline structure, colors range from greyish-brown to translucent with banded patterns, conchoidal fracture, specific gravity of 2.6 to 2.7.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, earthy to vitreous luster, cryptocrystalline structure, colors range from greyish-brown to translucent with banded patterns, conchoidal fracture, specific gravity of 2.6 to 2.7.
Formation & geological history
Formed in cavities in sedimentary or igneous rocks where silica-rich groundwater deposits microcrystalline quartz in concentric layers over millions of years.
Uses & applications
Used primarily in lapidary arts, decorative objects, jewelry, and prized by mineral collectors.
Geological facts
Geodes form when bubbles in volcanic rock or cavities in sedimentary rock fill with mineral-rich groundwater, slowly growing crystal linings from the outside in.
Field identification & locations
Often found in limestone formations, volcanic deposits, and riverbeds. Collectors typically spot them by their distinctive nodular shape and weathered, bumpy exterior.
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