The other day I tore up some track on the lowest level of the layout, that's been there for some 20 years. The track is Lionel tubular track 40-70 years old. When removing the accumulated dust, I first ran a magnet through it to gather up [recycle] any screws I had dropped. The magnet came out covered with a fine metallic powder and many short steel shards, finer than a hair. Too fine to be strands of wire, and of course any wire would have been copper and non-magnetic. The shards were about 1/4-3/8" long, and could not have been generated by any cutting. I also have not sanded the rails. The shards also make mean finger splinters.
I'm wondering what could have been the source. Anybody else out there experienced this?