mineral

Lake Superior Agate

Banded Chalcedony (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs. Color: Iron-stained red, orange, and tan with white banding. Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.60–2.64.

Hardness: 7 Mohs
Color: Iron-stained red, orange, and tan with white banding
Luster: Waxy to vitreous

Identified July 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed approximately 1.1 billion years ago during the Keweenawan Rift. Silica-rich groundwater deposited layers of quartz inside gas vesicles (bubbles) of cooling basaltic lava flows.

Uses & applications

Highly prized by collectors as a state gemstone, used in lapidary work for cabochons, jewelry, and decorative polished display pieces.

Geological facts

It is the official state gemstone of Minnesota. The distinctive red color is caused by the oxidation of iron that was present during the mineral's formation within volcanic rock.

Field identification & locations

Identify by looking for 'peeling' layers, translucent banding, and a waxy texture. Commonly found on beaches of Lake Superior, in gravel pits, and glacial till across Minnesota, Wisconsin, and Iowa.