mineral

Lake Superior Agate

Silicon Dioxide (SiO2) - Banded Chalcedony

AI-generated identification · may be incorrect

Hardness: 6.5 - 7 on the Mohs scale; Color: Red, orange, white, and tan concentric banding; Luster: Waxy to vitreous; Crystal system: Trigonal/Microcrystalline; Cleavage: None; Conchoidal fracture.

Hardness: 6
Color: Red, orange, white, and tan concentric banding
Luster: Waxy to vitreous

Identified July 25, 2026More mineral →

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Physical properties

Hardness: 6.5 - 7 on the Mohs scale; Color: Red, orange, white, and tan concentric banding; Luster: Waxy to vitreous; Crystal system: Trigonal/Microcrystalline; Cleavage: None; Conchoidal fracture.

Formation & geological history

Formed during volcanic activity about 1.2 billion years ago in the Midcontinent Rift System. Iron-rich silica-bearing groundwater filled gas cavities (vesicles) in ancient basalt lava flows, slowly precipitating chalcedony layers.

Uses & applications

Popular for lapidary work, jewelry (cabochons), tumbling, and mineral specimen collecting. Minnesota's official state gemstone.

Geological facts

Glaciers dispersed Lake Superior agates across Minnesota, Iowa, Wisconsin, and Michigan during the Ice Age, so they are frequently found far from their original source basalt beds.

Field identification & locations

Look for a pitted, iron-stained husk with concentric red, orange, and white bands exposed on worn surfaces or translucent edges under light. Commonly found in glacial till, riverbeds, and gravel pits in the Upper Midwest USA.