mineral

Lake Superior Agate

Cryptocrystalline Quartz (SiO2 with Iron impurities)

Hardness: 7 Mohs scale. Color: Brown, red, and orange tones caused by iron oxidation. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Cleavage: None (conchoidal fracture).

Hardness: 7 Mohs scale
Color: Brown, red, and orange tones caused by iron oxidation
Luster: Waxy to vitreous

Identified June 27, 2026More mineral →

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Physical properties

Hardness: 7 Mohs scale. Color: Brown, red, and orange tones caused by iron oxidation. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed approximately 1.1 billion years ago during the Midcontinent Rift System. Silica-rich fluids filled gas bubbles (vesicles) in volcanic basalt flows, slowly crystallizing into banded chalcedony.

Uses & applications

Highly prized by collectors as the official state gem of Minnesota; used in lapidary work for jewelry, cabochons, and decorative polished stones.

Geological facts

These are among the oldest agates in the world. Their distinctive red color comes from iron leached from local iron ores by groundwater during their billion-year history.

Field identification & locations

Identified by their characteristic waxy skin ('peel'), concentric banding, and translucent quality when held to light. Commonly found on beaches of Lake Superior or in glacial gravel pits across the Midwest.

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

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mineral