sedimentary
Lake Superior Agate
Silicon dioxide (Chalcedony)
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale, waxy luster, conchoidal fracture, and distinct red, brown, and yellow banding caused by iron oxides.
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Physical properties
Hardness of 7 on the Mohs scale, waxy luster, conchoidal fracture, and distinct red, brown, and yellow banding caused by iron oxides.
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan Rift Zone volcanism, where gas cavities in basalt filled with hydrothermal silica-rich fluids.
Uses & applications
Prized by lapidaries and collectors for cutting, polishing, and crafting into jewelry or decorative items.
Geological facts
These agates are the official state gemstone of Minnesota and feature concentric banding shaped by the thermal history of ancient lava flows.
Field identification & locations
Frequently found in glacial drift and gravel pits throughout Minnesota and neighboring states; identify by its characteristic fortification banding and waxy luster.
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