sedimentary
Lake Superior Agate
SiO2 (Quartz variety chalcedony)
AI-generated identification · may be incorrectHardness of 7 on Mohs scale, reddish-brown iron-stained exterior, waxy luster, and microcrystalline quartz structure.
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Physical properties
Hardness of 7 on Mohs scale, reddish-brown iron-stained exterior, waxy luster, and microcrystalline quartz structure.
Formation & geological history
Formed in gas cavities of basaltic lava flows over one billion years ago through the deposition of silica-rich groundwater.
Uses & applications
Commonly collected as a gemstone, tumbled, polished, and used in wire-wrapped jewelry.
Geological facts
They are the official state gemstone of Minnesota and display characteristic concentric banding patterns.
Field identification & locations
Identify in the field by their distinct reddish-brown color from iron oxide and waxy pitted surfaces, typically found in glacial drift throughout the upper Midwestern United States.
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Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
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Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
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Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary