mineral

Lake Superior Agate

Banded Chalcedony (SiO2)

Hardness: 7 on Mohs scale; Color: Red, orange, yellow, and white banding; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.60–2.64

Hardness: 7 on Mohs scale
Color: Red, orange, yellow, and white banding
Luster: Waxy to vitreous

Identified February 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift System. Silica-rich groundwater filled gas vesicles (bubbles) in cooling volcanic basalt flows, precipitating layers of quartz and iron impurities.

Uses & applications

Used in lapidary arts for jewelry, polished cabinet specimens, and as the official state gem of Minnesota. Industrial use is minimal compared to its value as a gemstone.

Geological facts

Lake Superior agates are distinguished by their rich iron-oxide staining, which gives them vibrant red and orange hues. They were distributed across the Midwest by the movement of glaciers during the last ice age.

Field identification & locations

Identify in the field by looking for 'peeling' layers, waxy luster when wet, and translucent banding. Commonly found in gravel pits, lake shores, and riverbeds in Minnesota, Wisconsin, Michigan, and Iowa.