gemstone

Lake Superior Agate

SiO2 (Quartz variety chalcedony)

Hardness of 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture, cryptocrystalline structure, specific gravity around 2.65, characterized by distinctive reddish-brown and orange banding caused by iron oxide staining.

Identified August 4, 2026More gemstone →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Keweenawan Rift Zone volcanic activity. Silica-rich groundwater filled gas cavities in basalt, depositing quartz in rhythmic layers over millions of years.

Uses & applications

Popular in jewelry, lapidary arts, and highly prized by rockhounds and mineral collectors.

Geological facts

Lake Superior agates are the official state gemstone of Minnesota. The distinctive red color comes from oxidized iron, which is abundant in the region's ancient volcanic rocks.

Field identification & locations

Commonly found in glacial drift, gravel pits, and along beaches in the Upper Midwest of the United States (such as near the given coordinates in Michigan and Minnesota). Look for waxy luster and concentric color bands.

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