mineral

Banded Agate (Lake Superior Agate / Sardonyx)

Silicon Dioxide (SiO2)

Hardness: 6.5 - 7 on Mohs scale. Color: Alternating bands of reddish-orange, brown, white, and translucent chalcedony. Luster: Waxy to vitreous. Crystal Structure: Trigonal/Microcrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified July 27, 2026More mineral →

Explore Banded Agate (Lake Superior Agate / Sardonyx) in the encyclopedia →

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Physical properties

Formation & geological history

Formed in silica-rich fluids filling gas cavities (vesicles) within ancient volcanic rocks around 1.1 billion years ago during the Midcontinent Rift System development.

Uses & applications

Used widely in lapidary arts, jewelry creation, cabochons, carved ornaments, and popular as a collectible gemstone.

Geological facts

Lake Superior Agate is the official state gemstone of Minnesota. The vivid red and orange hues are caused by varying amounts of iron oxides embedded in the microcrystalline quartz layers.

Field identification & locations

Identify by its distinctive fine parallel banding, waxy texture, translucency when backlit, and hardness (scratches glass). Found in gravel pits, lake shores, and river beds around the Lake Superior region and glacial drift areas.

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