I'm done lapping my stone, it was indeed quite easy to lap, stil took some effort because it was hollowed pretty bad. after it was flat I went up to grit 600 because I didn't have any finer grit laying around at the moment, after that I turned to lapping it on a other hone (Welsh slate) and the surface it becomming kind of reflective (at least more so then the Welsh slate).

I think my particular stone hasn't been used with oil that much, it's darker on the sides where oil came in from the sides and it is slightly porous (I noticed this when I put just a few drops of water on it and then spread these out, right after spreading these droplets there is a difference in darkness between initial spot and the rest, this difference quickly fades away)

besides al these observations it isn't as beautifull as the one from Modine