mineral

Lake Superior Agate

Quartz (Variety: Agate, SiO2)

Hardness: 7 on Mohs scale. Color: Shades of red, orange, and yellow due to iron oxide staining. Luster: Vitreous to waxy. Crystal structure: Trigonal (microcrystalline quartz/chalcedony). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 - 2.65.

Hardness: 7 on Mohs scale
Color: Shades of red, orange, and yellow due to iron oxide staining
Luster: Vitreous to waxy

Identified August 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich groundwater solutions into cavities in basaltic lava flows during the Midcontinent Rift volcanism approximately 1.1 billion years ago.

Uses & applications

Used primarily in lapidary arts for making jewelry, polished cabochons, and as prized specimens for rockhounds and collectors.

Geological facts

Lake Superior agates are the official state gemstone of Minnesota and are famous for their characteristic 'fortification' banding and rich red-orange colors caused by oxidized iron.

Field identification & locations

Found extensively in glacial drift and gravel pits around the Lake Superior region of North America. Look for waxy luster, conchoidal fractures, and concentric color banding when identifying in the field.