mineral
Lake Superior Agate
Silicon Dioxide (Cryptocrystalline Quartz), SiO2
Hardness: 7 (Mohs scale), Color: Bands of red, orange, yellow, and white caused by iron oxidation, Luster: Vitreous to waxy, Crystal Structure: Trigonal/Microcrystalline, No cleavage, Specific gravity: 2.6-2.64
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Physical properties
Hardness: 7 (Mohs scale), Color: Bands of red, orange, yellow, and white caused by iron oxidation, Luster: Vitreous to waxy, Crystal Structure: Trigonal/Microcrystalline, No cleavage, Specific gravity: 2.6-2.64
Formation & geological history
Formed roughly 1.1 billion years ago during the Midcontinent Rift. Gas bubbles trapped in cooling basaltic lava flows were later filled by silica-rich groundwater, depositing minerals layer by layer.
Uses & applications
Primarily used in jewelry, as gemstones for lapidary work, and highly prized by mineral collectors.
Geological facts
The Lake Superior Agate was designated as the official state rock of Minnesota in 1969. Unlike many other agates, its colors are primarily derived from iron extracted from the surrounding basalt.
Field identification & locations
Look for a waxy or glassy texture on broken surfaces and distinctive concentric banding. Often found on rocky beaches of Lake Superior or in glacial till across Minnesota, Wisconsin, and Michigan.
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