sedimentary
Lake Superior Agate
Silicon dioxide (chalcedony), SiO2
AI-generated identification · may be incorrectHardness of 6.5 to 7 on the Mohs scale, waxy luster, conchoidal fracture, and distinctive reddish-brown concentric banding caused by iron oxide staining.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy luster, conchoidal fracture, and distinctive reddish-brown concentric banding caused by iron oxide staining.
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan rifting event, where hydrothermal fluids deposited silica in gas cavities of basaltic lava flows.
Uses & applications
Primarily used as a lapidary stone for crafting polished cabochons, jewelry, and prized by recreational rock collectors.
Geological facts
These agates are the official state gemstone of Minnesota and feature characteristic hematite or iron staining derived from surrounding ancient soils.
Field identification & locations
Easily identified by concentric color bands of red, white, and brown with a waxy texture; commonly found in glacial drift, gravel pits, and beaches around the Upper Midwest of the United States.
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