mineral

Lake Superior Agate

Silicon dioxide (SiO2) - variety of Chalcedony

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Red, orange, tan, and brown banding caused by iron; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.60-2.65

Hardness: 7 Mohs scale
Color: Red, orange, tan, and brown banding caused by iron
Luster: Waxy to vitreous

Identified July 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift System. Gas bubbles in basaltic lava flows were filled by mineral-rich groundwater, depositing layers of silica and iron over time.

Uses & applications

Primarily used for jewelry, lapidary arts, and specimen collecting. It is the official state gemstone of Minnesota.

Geological facts

The distinctive red and orange colors are due to the presence of iron oxidation. They are often found in glacial drift throughout the Upper Midwest of the United States.

Field identification & locations

Identify in the field by looking for translucent, banded patterns often exposed by a waxy, pitted outer 'skin' or husk. Commonly found on beaches of Lake Superior, in gravel pits, and on dirt roads in Minnesota and Wisconsin.