sedimentary
Lake Superior Agate
Chalcedony (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, banded color patterns featuring reds, oranges, yellows, and browns due to iron oxide staining, cryptocrystalline structure, no cleavage, specific gravity of 2.58 to 2.64
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, banded color patterns featuring reds, oranges, yellows, and browns due to iron oxide staining, cryptocrystalline structure, no cleavage, specific gravity of 2.58 to 2.64
Formation & geological history
Formed in gas cavities of basalt lava flows through the deposition of silica-rich groundwater solutions over 1.1 billion years ago during the Keweenawan rifting event
Uses & applications
Used primarily in lapidary arts, jewelry making, and as a popular collectible specimen
Geological facts
These agates are the official state gemstone of Minnesota and are famous for their distinct, rich red and orange banding caused by oxidized iron
Field identification & locations
Found commonly in glacial drift, gravel pits, and along beaches around the Lake Superior region; identified easily by its concentric banding, waxy feel, and translucent edges
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