Yooperlites are rocks, specifically syenite rocks rich in fluorescent sodalite, found primarily along the shores of Lake Superior in Michigan’s Upper Peninsula. They appear as ordinary gray stones in daylight but glow vibrant orange, yellow, or pink under ultraviolet (UV) light, particularly 365nm longwave UV light, due to the fluorescence of sodalite. The name “Yooperlite,” trademarked by Erik Rintamaki, who discovered their glowing property in 2017, combines “Yooper,” a nickname for Upper Peninsula residents, and “lite,” referring to their luminescent quality. These rocks, formed from ancient volcanic activity and transported by glaciers from Canada’s Coldwell Alkaline Complex, are popular among rockhounds. They can be found on beaches like Whitefish Point, Grand Marais, or Little Girls Point, often after storms or in spring when ice shifts rocks. To hunt them, use a 365nm UV flashlight, scan slowly at twilight or night, and check near the water or high water mark.
[ref 1] (https://makeitmqt.com/what-is-a-yooperlite/)
[ref 2] (EGLE rockhound offers tips to find elusive, glowing ‘Yooperlites®’)
[ref 3] (Yooperlite : Properties, Formation, Uses, Locations » Geology Science)