sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, and colors ranging from brown, tan, and white to red, orange, and gray due to various impurities.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, and colors ranging from brown, tan, and white to red, orange, and gray due to various impurities.
Formation & geological history
Formed primarily within cavities of volcanic and metamorphic rocks through the deposition of silica-rich groundwater solutions in concentric layers over millions of years.
Uses & applications
Used widely in ornamental carvings, jewelry making, lapidary art, and as specimens for mineral and rock collectors.
Geological facts
Agates are often found lining or filling cavities in ancient lavas known as geodes. The banded patterns record changes in the solution chemistry during their slow formation.
Field identification & locations
Easily identified by its characteristic curved or concentric banding, waxy luster, and high hardness which allows it to scratch glass. Commonly found in riverbeds, beaches, and desert areas worldwide.
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