mineral

Lake Superior Agate

Silicon Dioxide (Chalcedony/Quartz), formula SiO2

Hardness of 6.5 to 7 on the Mohs scale. Colors include red, orange, and yellow due to iron oxide staining. Luster is vitreous to waxy. Cryptocrystalline structure with no cleavage and a conchoidal fracture. Specific gravity is approximately 2.60 to 2.65.

Identified August 1, 2026More mineral →

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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 fluids deposited microcrystalline quartz in gas cavities within basalt flows, creating concentric banding.

Uses & applications

Used primarily in lapidary arts, tumbled stones, wire-wrapped jewelry, and by mineral collectors.

Geological facts

Lake Superior agates are the official state gemstone of Minnesota. Their characteristic red and orange banding is caused by the oxidation of iron, with different bands reflecting changing groundwater conditions during formation.

Field identification & locations

Found primarily in the Upper Midwest of the United States (Minnesota, Wisconsin, Michigan). Identified in the field by its waxy luster, conchoidal fracture, and distinctive concentric color bands, often found weathered out in gravel pits, glacial drift, and riverbeds.

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Soil with Mineral Detritus and Quartz Fragments

Regolith / Silicate Mineral Aggregate

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Limonite / Goethite (Iron Ore Mineral nodule)

FeO(OH)·nH2O / FeO(OH)

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Schist

Metamorphic

Septarian Pebble

Septarian nodule / Concretion

sedimentary

Potassium Feldspar (Orthoclase)

Orthoclase (KAlSi3O8)

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