sedimentary
Chalcedony (Agate/Jasper Nodule)
Silicon Dioxide (SiO2)
Hardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, and specific gravity around 2.65.
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Physical properties
Hardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, and specific gravity around 2.65.
Formation & geological history
Formed through the deposition of silica-rich groundwater within cavities of volcanic or sedimentary rocks, typically over millions of years.
Uses & applications
Commonly used in lapidary arts, decorative carvings, gemstone jewelry, and collected by rockhounds.
Geological facts
Chalcedony is a cryptocrystalline form of silica, comprising fine intergrowths of quartz and moganite. It has been used since antiquity to create intaglios, seals, and ornamental objects.
Field identification & locations
Identified in the field by its conchoidal fracture, waxy luster, and resistance to scratching by steel. Frequently found in regions with historical volcanic activity or river gravels.
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