Oh Geez, talk about missing vital visual details. I took a look on the computer instead of the phone today... Didn't even see the surface scratching or slurry last night. Definitely not an Ark, it does look like some type of slate. Is that a crack in the side maybe along a sedimentary layer? That would definitely indicate a slate stone. The comment that it was a hard stone threw me. Hard stone means something much different to me, lol. You would never be able to put scratches in a "hard" stone like in the surface of that one, nor slurry it well with a rubbing stone that wasn't made of diamond! If it's an Escher or Thuri I would definitely call those very soft stones.