mineral
Lake Superior Agate
Silicon Dioxide (Chalcedony), SiO2
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale, reddish-brown color due to iron oxide staining, waxy to vitreous luster, and microcrystalline trigonal structure.
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Physical properties
Hardness of 7 on the Mohs scale, reddish-brown color due to iron oxide staining, waxy to vitreous luster, and microcrystalline trigonal structure.
Formation & geological history
Formed roughly 1.1 billion years ago when hydrothermal fluids deposited quartz in gas vesicles of basaltic lava flows.
Uses & applications
Prized by lapidaries and collectors for cutting into cabochons, polishing, and crafting into unique jewelry.
Geological facts
They are the official state gemstone of Minnesota and feature characteristic concentric banding formed by rhythmic precipitation.
Field identification & locations
Identify in the field by their distinct iron-stained reddish exteriors, curved conchoidal fractures, and embedded quartz-filled banding. Commonly found in glacial drift throughout the upper Midwestern United States.
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