sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, colors include white, gray, blue, red, orange, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) crystal structure with no visible cleavage, specific gravity of 2.58 to 2.64.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, colors include white, gray, blue, red, orange, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) crystal structure with no visible cleavage, specific gravity of 2.58 to 2.64.
Formation & geological history
Formed mainly in cavities of eruptive rocks or ancient lavas through the deposition of silica from groundwater solutions over millions of years.
Uses & applications
Used in ornamental objects, jewelry, carving, making mortars and pestles for laboratories, and highly sought after by rockhounds and mineral collectors.
Geological facts
Agates often display distinct concentric banding patterns created by alternating layers of microscopic quartz crystals, named after the Achates River in Sicily where they were found in antiquity.
Field identification & locations
Identified by its characteristic conchoidal fracture, waxy luster, and banded patterns. Commonly found worldwide in volcanic rock cavities, particularly in Brazil, Uruguay, and the western United States.
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