sedimentary
Lake Superior Agate
Chalcedony (Microcrystalline Quartz, SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Red, orange, tan, and white. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Specific gravity: 2.6-2.64.
- Hardness
- 6
- Color
- Red, orange, tan, and white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Red, orange, tan, and white. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Specific gravity: 2.6-2.64.
Formation & geological history
Formed approximately 1.1 billion years ago during the Midcontinent Rift. Gas bubbles trapped in cooling basaltic lava flows were later filled with silica-rich groundwater, depositing minerals in layers.
Uses & applications
Commonly used for lapidary work, jewelry making (cabochons), and as a highly sought-after collector's item in the Midwest United States.
Geological facts
The Lake Superior Agate was designated as the official state gem of Minnesota in 1969. Each agate is unique, with some displaying 'eyes' or distinct fortification banding.
Field identification & locations
Identify by looking for waxy luster, translucency when held to light, and characteristic concentric banding or pitted 'peel' texture. Commonly found on beaches and in gravel pits across Minnesota, Wisconsin, and Michigan.
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