I bought a hone from a flea market, but I couldn't indentify which kind of rock is it. It was in very bad shape, deep scracthes everywhere, but I could feel that it is a fine hone with my fingernail. I could see saw marks on the side, so I thought that it is a natural stone. I made a few photos, maybe someone can tell me what kind of stone it is. The surface feels silky smooth after lapping, nearly as smooth as my CH12k, it was easy to medium hard to lap. As you can see on the photos, it looks like there are shiny little particles in the stone.