mineral

Lake Superior Agate

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Iron-stained red, orange, and tan with translucency; Luster: Vitreous to waxy; Crystal structure: Hexagonal (microcrystalline/cryptocrystalline crypto-fibrous); Specific Gravity: 2.6-2.65.

Hardness: 6
Color: Iron-stained red, orange, and tan with translucency
Luster: Vitreous to waxy

Identified June 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift. Gas bubbles trapped in basaltic lava flows were filled by silica-rich groundwater, resulting in concentric banding.

Uses & applications

Primarily used for lapidary work, jewelry (cabs/beads), and as a highly sought-after collector's item in the Great Lakes region.

Geological facts

Designated as the official state rock of Minnesota in 1969. The red color is caused by the oxidation of iron that seeped into the silica during formation.

Field identification & locations

Look for a waxy texture, translucent bands, and 'pitting' on the exterior surface. Found mostly in glacial till or gravel pits throughout Minnesota, Wisconsin, and Michigan.