mineral

Lake Superior Agate

Silicon Dioxide (SiO2) - Variety Agate

Hardness: 7 on Mohs scale; Color: Red, orange, yellow, and brown due to iron impurities; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline quartz; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58–2.64.

Hardness: 7 on Mohs scale
Color: Red, orange, yellow, and brown due to iron impurities
Luster: Waxy to vitreous

Identified May 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed in gas vesicles (bubbles) within basaltic lava flows approximately 1.1 billion years ago during the Midcontinent Rift. Iron-rich silica-bearing waters filled these cavities, depositing layers of quartz over time.

Uses & applications

Highly valued by gemstone collectors, lapidary artists for jewelry (cabs, pendants), and decorative polishing.

Geological facts

The Lake Superior Agate was designated the official state gem of Minnesota in 1969. The red and white banding is its most iconic feature, distinguished from other agates by its unique iron carbonate staining.

Field identification & locations

Identify by looking for waxy luster, quartz-filled banding, and 'eyes' on a weathered surface. Common in gravel pits, beaches, and riverbeds across the Upper Midwest USA (MN, WI, MI, IA).

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