mineral
Lake Superior Agate
Silicon Dioxide (SiO2) - Banded Chalcedony
Hardness: 6.5-7 on Mohs scale; Color: Red, orange, white, tan, and brownish tones caused by iron inclusions; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (trigonal); Cleavage: None, exhibits conchoidal fracture.
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Red, orange, white, tan, and brownish tones caused by iron inclusions; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (trigonal); Cleavage: None, exhibits conchoidal fracture.
Formation & geological history
Formed approximately 1.1 billion years ago during the Midcontinent Rift System in North America. Silica-rich water deposited fine layers of quartz inside gas cavities (vesicles) of basaltic lava flows.
Uses & applications
Popular for lapidary work, jewelry (cabochons, pendants), decorative displays, and tumbling. Highly sought after by mineral collectors.
Geological facts
Lake Superior agate is the official state gemstone of Minnesota. Its rich red and orange colors are caused by varying amounts of iron oxidation.
Field identification & locations
Look for a polished, waxy exterior with fine concentric banding or peel-like layers of red, white, and orange, often found weathered along gravel pits, lake shores, and river beds in the Upper Midwest of North America.
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