The elusive Lake Superior agate. Rockhounds scour Lake Superior’s shoreline for these rare banded beauties—from the western reaches of the Keweenaw Peninsula to the U.P.’s easternmost Whitefish Point.

Watch as a rare fluorescent treasure hunt unfolds on the shores of Lake Superior where ordinary rocks hide a dazzling secret under UV light. Erik Rintamaki, a tour guide from Michigan, USA, takes ...