sedimentary
Agate / Chalcedony Geode
Silicon Dioxide (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, and a specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, and a specific gravity around 2.60 to 2.65.
Formation & geological history
Formed in cavities of volcanic and sedimentary rocks where silica-rich groundwater deposited microscopic quartz crystals in concentric layers over millions of years.
Uses & applications
Commonly used for lapidary arts, ornamental objects, jewelry, and prized as specimens by mineral collectors.
Geological facts
Agate geode formations often start as gas bubbles in lava or animal burrow voids in sedimentary rock, gradually being filled mineral by mineral as fluids percolate through.
Field identification & locations
Can be identified in the field by its distinct banded layers, waxy luster, and resistance to scratching by a steel knife. Found worldwide, particularly in regions with historical volcanic activity.
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