DULUTH — The rest of the beachgoers, dog walkers and rock hoppers had cleared out Friday night, when Christopher Wenner was just getting started. Bent at the waist, and scanning the rocks on Duluth's Brighton Beach with a black-light flashlight, Wenner claimed small victories nearly everywhere he searched.
“There’s a piece right there!”
“Here’s a beauty.”
“That’s a nice vein.”
All of his exclamations related to the minerals aglow in the ultraviolet light. A lifelong gem and mineral hunter, Wenner searched the rocks for a fluorescent mineral he’s uncovered along the North Shore, and he’s calling it “Illumilyte.”
“Because when you shine it at night on all the rocks, some of them glow red like embers in a fire,” the 51-year-old finishing carpenter said.
Wenner carried a box of beach rocks he’d previously collected, and justified his enthusiasm with a demonstration. Under the ultraviolet light, the rocks “popped” alive — some with spots glowing red from their core. Others revealed fluorescent galaxies contained in the handheld rocks, as if the stones contained nebulas like the bottle held the city of Kandor in the Superman comics.
“I’ve been enjoying this for over a year or so now,” Wenner said. “I kind of want to bring it to light. It’s a new twist to rock hunting.”
In Michigan, rock hunters have been smitten with its Yooperlite rocks — fluorescent rocks used to draw tourists and their black lights, so they can observe the rich orange and yellow glows contained in the beach rocks there.
But what Wenner is onto along the North Shore of Lake Superior is different. He sought University of Minnesota Duluth geologist Fred Davis, a professor in the Earth and Environmental Sciences Department, to find out just what it was.
The Yooperlite contains the rich blue mineral sodalite, which glows orange and yellow under a black light. But when Davis tested one of Wenner’s rocks with a drip of mild acid onto the samples, the rocks fizzed and Davis knew he was looking at calcite, a mineral that reacts to the acid in such a manner.
“I didn’t immediately know what it was,” Davis said. “I had not considered that was a thing you could do on the North Shore before he came to my office.”
Fluorescence in minerals is a known phenomenon. Clubs sprout up around it and one can search Google to find people who are excited about it.
Wenner has uncovered it in the basalt rocks that make up the local beaches.
"A lot of us walk along the beach all our lives and never see it," Wenner said.
A billion years ago
Davis described how it all started a billion years ago.
The basalt rocks are volcanic leftovers from the Midcontinent Rift — a dynamic period of land formation in the middle of North America. Over the ensuing eon, gases trapped in the rocks would freeze and create porous rocks, somewhat like the more exaggerated qualities of pumice stones.
The pockets have been infiltrated by water and fluids containing carbon dioxide which leaves mineral deposits behind, Davis explained — in this case, calcite.
“What I think is interesting about it is that folks already come to Duluth because they’re interested in rocks,” Davis said. “They may not know this is happening here, and might be interested to know there’s something in addition to the agates.”
Agate hunting at 5 years old with his grandmother, Mildred Schulenberg, is how Wenner’s pursuit of rock collecting got started. He’s been doing it now for more than 45 years. He has panned for gold in Alaska, sought aquamarine in Colorado, and, generally, cast his glances underfoot, where the world, for him, comes to life.
“We’ve got boxes of rocks in our living room, in the shed, in the extra bedroom,” his wife, Daina Mirsch-Wenner, said of their home. “They’re all over.”
As Wenner and his family strode the beach, the ships’ wakes hit the beach and wet the rocks along the line Wenner likes to look for his stones.
One in hand, he noted its dimming effect before burning out.
“See that?” he said. “It glows after you shut the light off. The light bounces around in there.”
Of course, under blacklight, the beach pops to show all sorts of other things, too — a piece of gum, bird scat, boot prints on rocks, algae ... but Wenner is keen to the deeper glow of the fluorescence.
The calcite, he said, runs through the entire rock, not just on the surface. He’s found it in large boulders, too, but prefers the smaller rocks he can keep as trophies.
"You get pickier the more you collect," he said.
Originally, he wanted to call the phenomenon "firelyte," but found the word to be trademarked. He and Daina have decided on describing the phenomenon as "illumilyte."
“There’s a piece right there,” Wenner said. “It almost looks like a charcoal briquette.”