BRIMLEY (AP) — The Upper Peninsula has fluorescent minerals that glow when placed under UV light.

Brimley resident Erik Rintamaki collects and sells the rocks, which he’s named “yooperlites,” MLive reported. Rintamaki also leads tours with a UV light where he shows others how to spot them.

Rintamaki is credited with discovering this specific variation of sodalite in June 2017.

“I left for the beach at 4 a.m. and arrived just in time to use my cheap 3 LED longwave UV flashlight,” he said. “I found two very small yooperlites about the size of a dime. I went four more times and only found a half dozen stones.”

Rintamaki was able to find more rocks by upgrading his LED UV light.

“Now I have upgraded even further to Convoy S2+ UV and a shortwave lamp,” he said. “So I hope to open even more secrets of our Lake Superior beaches.”

Testing conducted at Michigan Tech University found that the rocks have sodium, aluminum, silicon, chlorine and oxygen, but no structural sulfur, which likely results in the fluorescent properties of the mineral, said Kevin Cole, an associate professor of geology at Grand Valley State University.

Such rocks were likely left behind by glaciers centuries ago and rounded by Lake Superior’s waves, researchers said.