mineral

Banded Agate (Lake Superior Agate)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown, tan, and dark brownish-red banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Grayish-brown, tan, and dark brownish-red banding
Luster: Waxy to vitreous

Identified July 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed approximately 1.1 billion years ago during the Midcontinent Rift System. Silica-rich solutions precipitated layer by layer within gas vesicles (cavities) in ancient basaltic lava flows.

Uses & applications

Popular for lapidary work, jewelry making (cabochons, beads), rock tumbling, and ornamental specimen collecting.

Geological facts

Lake Superior agate is the official state gemstone of Minnesota. The distinctive banding represents successive layers of chalcedony deposition, often colored by trace amounts of iron oxides.

Field identification & locations

Identified in the field by fine, concentric or parallel color banding, a waxy feel when smooth, and high hardness (scratches glass). Commonly found along beaches, gravel pits, and riverbeds in the Lake Superior region and glaciated areas of the Upper Midwest US.

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