mineral

Lake Superior Agate

Chalcedony (cryptocrystalline Quartz, SiO2) with iron oxide inclusions

Hardness: 7 Mohs; Color: Rich red, orange, and white bands; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Hardness: 7 Mohs
Color: Rich red, orange, and white bands
Luster: Vitreous to waxy

Identified June 15, 2026More mineral →

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Physical properties

Hardness: 7 Mohs; Color: Rich red, orange, and white bands; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Formation & geological history

Formed roughly 1.1 billion years ago during the Keweenawan Rift in gas vesicles of basaltic lava flows. Iron leached from surrounding rocks provided the vibrant red and orange coloration.

Uses & applications

Highly prized by collectors and lapidarists; used in jewelry (cabochons), tumbling, and decorative arts. It is the official state gem of Minnesota.

Geological facts

Lake Superior Agates are unique for their rich iron-derived coloring. They were dispersed across the Midwest by the Laurentide Ice Sheet during the last glacial period.

Field identification & locations

Identify in the field by looking for translucent banded patterns, pit-marked 'peeling' rinds, and waxy luster when wet. Common in gravel pits, lake shores, and riverbeds in Minnesota, Wisconsin, and Michigan.

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