mineral
Lake Superior Agate
Silicon Dioxide (SiO2) - variety of Chalcedony
Hardness: 6.5-7.0 (Mohs scale), Color: Red, orange, tan, and white bands/patches, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Translucent to opaque
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.0 (Mohs scale), Color: Red, orange, tan, and white bands/patches, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Translucent to opaque
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan Rift when gas bubbles in basaltic lava flows were filled by mineral-rich groundwater, depositing thin layers of silica and iron oxides.
Uses & applications
Primarily used for gemstone collecting, jewelry (cabochons), and lapidary art due to its beautiful banding patterns and durability.
Geological facts
Designated as the official state gemstone of Minnesota in 1969; the coloring is primarily due to iron oxidation (limonite and hematite) during formation.
Field identification & locations
Commonly found on the shores of Lake Superior and in glacial drift throughout the Upper Midwest. Identify by its iron-rich red coloring and waxy translucency when wet.
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