sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including white, gray, blue, red, orange, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including white, gray, blue, red, orange, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed mainly in cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions in concentric layers over long periods.
Uses & applications
Used in ornamental objects, jewelry, polished specimens, mortar and pestle sets, and as a popular collector mineral.
Geological facts
Agate is one of the most popular stones used in art and lapidary work. It was named by Theophrastus, a Greek philosopher, after the Achates river in Sicily.
Field identification & locations
Easily identified by its characteristic banded patterns and waxy luster. Common in volcanic regions worldwide, particularly in Brazil, Uruguay, India, and the western United States.
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