The Wolfsegg Iron is a lump of iron found inside a block of coal at a mine in the Austrian village of Wolfsegg. The scientific journal Nature describes it as “almost a cube” with a “deep incision” running around it. It weighs about 1.7 pounds.

It’s not at all clear where it can have come from. A meteorite would not have such an artificially cubical shape, and prehistoric civilizations should not have had the technology to make such a thing.

After a thorough examination in 1966, researchers at Vienna’s Natural History Museum concluded that the block is simply man-made cast iron, perhaps used as ballast in primitive mining machinery. But no other such blocks have ever been found.