gemstone
Lake Superior Agate
Silicon dioxide (Chalcedony), SiO2
AI-generated identification · may be incorrectHardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, distinct concentric color banding in reds, oranges, and yellows, with a cryptocrystalline structure.
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Physical properties
Hardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, distinct concentric color banding in reds, oranges, and yellows, with a cryptocrystalline structure.
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan Rift Zone volcanism, as hydrothermal fluids deposited silica within gas cavities of basalt.
Uses & applications
Prized as a lapidary gemstone, cut and polished into cabochons, and heavily collected by hobbyists in the Upper Midwest.
Geological facts
It is the official state gemstone of Minnesota and features iron-rich banding caused by fluctuating groundwater chemistry during formation.
Field identification & locations
Easily identified in the field by its waxy luster, conchoidal fracture, and striking red-orange concentric fortification bands; commonly found in glacial drift and gravel pits.
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