sedimentary
Agate Nodule
Silicon Dioxide (Chalcedony / Quartz), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, colors typically include brown, tan, yellow, or white due to iron oxide impurities, and conchoidal fracture with no true cleavage.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, colors typically include brown, tan, yellow, or white due to iron oxide impurities, and conchoidal fracture with no true cleavage.
Formation & geological history
Formed through the deposition of silica from groundwater solutions in the cavities of ancient volcanic or sedimentary rocks, often developing in concentric bands over millions of years.
Uses & applications
Used primarily in lapidary arts, decorative items, jewelry making, and as collector specimens.
Geological facts
Agate has been used since antiquity for ornamentation, seals, and protective amulets. The name comes from the Achates River in Sicily where agates were found in ancient times.
Field identification & locations
Can be identified in the field by its waxy luster, conchoidal fracture, characteristic weathering rind, and translucent edges where broken. Commonly found in riverbeds, gravel deposits, and volcanic regions worldwide.
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