mineral

Lake Superior Agate

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Red, orange, brown, and tan stripes; Luster: Vitreous/Waxy; Crystal Structure: Trigonal (microscopic); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Red, orange, brown, and tan stripes
Luster: Vitreous/Waxy

Identified May 12, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Red, orange, brown, and tan stripes; Luster: Vitreous/Waxy; Crystal Structure: Trigonal (microscopic); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7

Formation & geological history

Formed approximately 1.1 billion years ago during the Midcontinent Rift System in North America. Iron-rich silica-bearing waters filled gas bubbles (vesicles) in volcanic basalt, depositing microscopic layers of chalcedony over time.

Uses & applications

Commonly used for jewelry (cabochons), lapidary art, and specifically as a highly sought-after state gemstone for Minnesota.

Geological facts

The distinctive red color is caused by the oxidation of iron. These agates were spread across the Midwest by glaciers during the last Ice Age, meaning they are often found far from their original volcanic source.

Field identification & locations

Identify in the field by looking for waxy luster, 'peeling' layers, and translucent red or orange banding. They are commonly found in gravel pits, lake shores, and riverbeds across Minnesota, Wisconsin, and Michigan.