sedimentary
Lake Superior Agate
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Red, orange, tan, and white banding, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Specific Gravity: 2.6-2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Red, orange, tan, and white banding, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Specific Gravity: 2.6-2.65
Formation & geological history
Formed approximately 1.1 billion years ago during the Keweenawan Rift. Gas bubbles in basaltic lava flows were filled by silica-rich groundwater, depositing minerals layer by layer.
Uses & applications
Highly prized by collectors, used in jewelry (lapidary), cabochons, and as state gemstones (Minnesota).
Geological facts
The Lake Superior Agate is the official state gemstone of Minnesota. Its unique red and orange hues come from iron leached from the surrounding volcanic rocks.
Field identification & locations
Identified by 'peeling' layers, smooth waxy texture, and concentric bands. Commonly found on beaches of Lake Superior, gravel pits, and glacial till across the Midwest.
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