mineral

Lake Superior Agate

Chalcedony (cryptocrystalline Quartz), SiO2

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Red, orange, and tan bands from iron impurities; Luster: Vitreous to waxy; Crystal structure: Hexagonal (trigonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.58–2.64

Hardness: 7 on Mohs scale
Color: Red, orange, and tan bands from iron impurities
Luster: Vitreous to waxy

Identified July 4, 2026More mineral →

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Physical properties

Formation & geological history

Formed in gas vesicles of lava flows approximately 1.1 billion years ago during the Midcontinent Rift. Silica-rich groundwater filled these cavities, depositing layers of chalcedony over time.

Uses & applications

Highly prized by collectors; used in jewelry, lapidary arts, and as the official state gemstone of Minnesota.

Geological facts

The distinctive red color comes from iron leached from local rocks during the silica deposition. They were spread across the Midwest by glaciers during the last Ice Age.

Field identification & locations

Identify by looking for concentric 'banding' or ring patterns and a waxy texture. Commonly found on beaches of Lake Superior, gravel pits, and riverbeds across Minnesota, Wisconsin, and Iowa.