Twinkle, Twinkle, Little Stone!

Rock hunting at night for fluorescent treasures.
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Upper Peninsula rockhound Erik Rintamaki discovered rocks that glow under ultraviolet light on a Lake Superior shoreline at night while searching for agates.
Upper Peninsula rockhound Erik Rintamaki discovered rocks that glow under ultraviolet light on a Lake Superior shoreline at night while searching for agates.

These days, most who walk the Lake Superior shoreline at night aren’t looking for starry glimmers in the sky but on the ground. They are scanning the beaches with ultraviolet flashlights, hoping to spot newly recognized fluorescent rocks — popularly known as Yooperlites — which glow with ember-like flecks and streaks of orange.

Their story begins thousands of years ago when glaciers carried them down from a rock formation called the Coldwell Complex on the Canadian side of Lake Superior, said Theodore Bornhorst, Ph.D., professor of geology and executive director of Michigan Technological University’s A.E. Seaman Mineral Museum. The formation includes a rather unusual variety of the mineral sodalite — one that fluoresces orange under longwave ultraviolet light.

When the glaciers melted back, they left pebbles, cobbles and boulders of this rock scattered throughout all the gravels in this area,” he said. 

But it wasn’t until a dark night in June 2017 that anybody really took notice. That’s when self-described rockhound and Yooper Erik Rintamaki went to the beach armed with a UV flashlight. He hoped to find semiprecious gemstones known as Lake Superior agates, some of which softly fluoresce under UV radiation. He had no luck with agates, but something else caught his eye.

I was on my hands and knees, and at 4 o’clock in the morning, I found three little bright orange-glowing stones — one had a flower pattern on it, one had little stars all over it and one had lines going through it,” he recalled.

Upper Peninsula rockhound Erik Rintamaki discovered rocks that glow under ultraviolet light on a Lake Superior shoreline at night while searching for agates.Over the next year, geologists suspected, and tests finally confirmed that the stones’ fluorescence was coming from sodalite, leading to:

Mineral News calling Rintamaki’s findthe first verified sodalite documented from the state of Michigan.” He trademarked the name “Yooperlites” for the stones and eventually quit his long-held job in a local casino to go into the Yooperlite business, promoting and selling the stones, and leading tours.

Bornhorst said the night search for these glowing rocks has caught on. A wide variety also is on display at the A.E. Seaman Mineral Museum.

You can go out, find a few, take them home, use your black light to show some people, and it’s a good story about your Upper Peninsula adventure,” he said. “And the current craze has left more agates on the beaches to be found during the daylight hours. Everybody’s happy.

— Leslie Mertz, Michigan BLUE Magazine.


WHERE TO GO: 

To find the fluorescing stones, Erik Rintamaki recommends Lake Superior beaches anywhere “from Whitefish Point west.” Theodore Bornhorst suggests scouring the Keweenaw Peninsula shoreline from Copper Harbor to Ontonagon. Prime picking comes in early spring after winter ice picks up stones from deeper water and transports them to the beach.

For more information about minerals, check out the A.E. Seaman Mineral Museum (museum.mtu.edu). Rintamaki’s Yooperlite tours are available at store.yooperlites.com/pages/yooperlite-tours.

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