I found a lump of Ferro-molybdenum up near Hazard Mine in Castleton once - it was black and sharp and spiky-looking, and I thought it was a meteorite as it was embedded in the ground. I became suspicious though when I also found some lumps of multi-coloured glassy slag nearby. Anyway I took it home and cleaned it up under the tap, which took ages and produced loads of dark blue 'ink'. Once it was shiny and silver my mate took it to a guy he knew at Outokumpo with a XRF meter and he told us what it was. I've still got it, but it's sort of yellowed and lost some of its lustre now, but it's very sharp-looking, like a piece of curved flint. At least it's not radioactive...
Anyway, I suspect it was related to the notorious paper-pulp 'soil improvement' episode caused by a less-than-scrupulous landowner.