Has anyone ever heard of a graphite hone. I picked up a 3 lot of hones on Ebay. I only wanted the confirmed "Tytex Carbo42". But one of the others is very puzzling. It is 4 x 2 x 3/8 inches thick. It is black in color and very soft, and has a slight sheen to it, similar to pencil lead. I can actually write with it on a piece of paper. Any ideas??