sedimentary
Lake Superior Agate
Silicon dioxide (chalcedony var. agate), SiO2
AI-generated identification · may be incorrectHardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture, and distinct red, brown, and yellow concentric banding caused by iron oxides.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture, and distinct red, brown, and yellow concentric banding caused by iron oxides.
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan Rift phase by mineral-rich hydrothermal fluids depositing silica in gas cavities of basalt flows.
Uses & applications
Primarily collected as a lapidary material, cut and polished for jewelry, and prized by amateur rockhounds.
Geological facts
It is the official state gemstone of Minnesota and features characteristic iron-oxide banding unique to the glacial drift of the Upper Midwest.
Field identification & locations
Found widely in glacial gravels and riverbeds across Minnesota, Wisconsin, and Michigan; identify by its waxy luster, curved banding, and translucent edges.
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