sedimentary
Banded Agate (specifically Lake Superior Agate or similar)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 6.5 - 7 mohs; Color: Red, orange, white, and translucent; Luster: Vitreous to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64
- Hardness
- 6
- Color
- Red, orange, white, and translucent
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5 - 7 mohs; Color: Red, orange, white, and translucent; Luster: Vitreous to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64
Formation & geological history
Formed roughly 1.1 billion years ago during the Keweenawan Rift. Formed by silica-rich groundwater filling gas bubbles (vesicles) in volcanic basalt flows.
Uses & applications
Commonly used in lapidary work for cabochons, jewelry, collections, and occasionally as structural bearings in precision instruments due to its hardness.
Geological facts
Lake Superior Agates are the Minnesota state gemstone. They are known for their rich red and orange colors, which come from oxidized iron (hematite) present during formation.
Field identification & locations
Identify by looking for waxy luster, 'eye' patterns, or parallel banding on weathered surfaces. Frequently found in glacial till, gravel pits, and along shorelines of the Great Lakes.
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