sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5-7 on the Mohs scale. Colors vary widely including white, gray, blue, red, orange, and brown, often with banded patterns. Luster is waxy to vitreous. Cryptocrystalline crystal structure with conchoidal fracture.
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Physical properties
Hardness of 6.5-7 on the Mohs scale. Colors vary widely including white, gray, blue, red, orange, and brown, often with banded patterns. Luster is waxy to vitreous. Cryptocrystalline crystal structure with conchoidal fracture.
Formation & geological history
Formed mostly within cavities of volcanic and metamorphic rocks by the deposition of silica from groundwater solutions over millions of years.
Uses & applications
Used for ornamental objects, jewelry, polished specimens, mortars and pestles in laboratories, and as collector items.
Geological facts
Agate is one of the most popular stones used in art and healing. The ancient Greeks and Romans used agates for signet rings and medicinal amulets.
Field identification & locations
Found worldwide in volcanic rock cavities or weathered out in river gravels. Easily identified by its distinct concentric banding and waxy luster.
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