In the early 17th century, fur traders traversing Lake Superior in North America heard tales of a fabulous boulder lying on the banks of the Ontonagon River. The boulder was said to be five tones in weight and as large as a house. And it was made of solid copper.

Stories about such a prize lying unclaimed in the wild set off many prospectors in the hunt, and it wasn’t long before the boulder was located. It really was made of solid copper. Curiously, no effort was made to relocate the treasure until nearly two centuries later. In 1766, when trader Alexander Henry laid eyes on the rock he was so excited that he grossly overestimated the weight of the boulder to be ten tons. Henry reported that the copper was so pure and malleable that he was able to easily remove a large piece.

A 19-ton piece of native copper displayed at the A. E. Seaman Mineral Museum of Michigan Technological University. Photo credit: Michigan Technological University