mineral

Banded Agate (specifically Lake Superior Agate)

Silicon dioxide (SiO2) - Cryptocrystalline Chalcedony

Hardness: 6.5-7 (Mohs scale); Color: Banded layers of red, orange, tan, and white; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Banded layers of red, orange, tan, and white
Luster: Vitreous to waxy

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift System in North America. Silica-rich groundwater filled gas bubbles (vesicles) in volcanic basalt, depositing minerals layer by layer to create rhythmic bands.

Uses & applications

Commonly used for lapidary work (cabochons), jewelry, decorative tumbling, and as a popular collectible specimen for hobbyists.

Geological facts

Lake Superior Agates are the state rock of Minnesota. The red color is caused by iron oxidation (limonite and hematite) that leached into the stone during formation.

Field identification & locations

Identify in the field by looking for 'peeled' surfaces that show concentric banding and a waxy texture. Found widely in glacial drift across Minnesota, Wisconsin, and Michigan. Best found in gravel pits or along lake shores after a rain.

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