On the frigid day I visited, Kennedy took me to Pea Ridge's core room, a metal shed stuffed with stacks of long, thin cardboard boxes. Inside each box is a section of a core sample taken when the mine was first developed. The one-inch-diameter cylindrical rocks helped Bethlehem Steel, the original owner, determine what the mine had to offer. Back in the 1960s, however, they were only interested in iron. Kennedy pulled out a broken piece and held a magnet to it, and it stuck — a chunk of magnetite, just like the front office sentinel. Another slice of rock was embedded with some glinting yellowish speckles. Those could be bits of rare earth oxides, he said.