Yooperlite (Sodalite-bearing Syenite)

Physical Properties

Hardness: 5.5-6 (Mohs); Color: Gray or mottled under normal light, bright orange-yellow under UV light (365nm); Luster: Dull to vitreous; Crystal structure: Hexagonal/Isometric inclusions; Specific gravity: 2.6-2.7

Formation & Geological History

These are glacial erratic rocks originally from the alkaline igneous complexes of the Canadian Shield, specifically Coldwell Complex in Ontario, deposited in the Great Lakes region by glaciers during the last Ice Age.

Uses & Applications

Primarily used for mineral collecting, lapidary work (polishing and cabochons), and as a novelty for fluorescent mineral enthusiasts.

Geological Facts

The name 'Yooperlite' was trademarked by Erik Rintamaki who 'discovered' them on the shores of Lake Superior in 2017. The fluorescence is caused by the presence of fluorescent sodalite.

Field Identification & Locations

Identify using a long-wave 365nm UV flashlight at night; look for grainy, salt-and-pepper textures in daylight. Most commonly found along the rocky beaches of Lake Superior in Michigan's Upper Peninsula.

Identified on: 5/10/2026

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