sedimentary
Chalcedony Nodule / Agate
Silicon Dioxide (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.58 - 2.64, and typically exhibits brownish, grayish, or bluish tones with weathered outer skin.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.58 - 2.64, and typically exhibits brownish, grayish, or bluish tones with weathered outer skin.
Formation & geological history
Formed in low-temperature hydrothermal environments or as cavity fillings in volcanic and sedimentary rocks where silica-rich groundwater precipitates quartz microcrystals over millions of years.
Uses & applications
Used in lapidary arts, ornamental carvings, gemstone jewelry, and as a popular specimen for mineral collectors.
Geological facts
Chalcedony nodules often form in gas bubbles within volcanic lavas, later weathering out of the surrounding rock as extremely durable pebbles due to their high resistance to erosion.
Field identification & locations
Can be identified in the field by its waxy luster, conchoidal fracture, and characteristic bumpy or botryoidal nodular exterior. Commonly found in riverbeds, gravel deposits, and volcanic regions worldwide.
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