sedimentary
Lake Superior Agate
Silicon Dioxide (Chalcedony), SiO2
AI-generated identification · may be incorrectMohs hardness of 7, vitreous luster, cryptocrystalline structure, exhibits distinct red, orange, and brown iron-oxide banding.
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Physical properties
Mohs hardness of 7, vitreous luster, cryptocrystalline structure, exhibits distinct red, orange, and brown iron-oxide banding.
Formation & geological history
Formed roughly 1.1 billion years ago via hydrothermal precipitation of silica within gas cavities of Keweenawan basalt flows.
Uses & applications
Used primarily in lapidary arts, jewelry, and polished collector specimens.
Geological facts
Glacial action transported these agates across the Upper Midwest, making them the official state gemstone of Minnesota.
Field identification & locations
Identified by waxy luster, conchoidal fracture, and concentric color banding; found primarily in gravel pits and glacial drift.
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