ID of old barber hone

[Kristian]

Hello.
Could anyone please help me ID this old stone, I got from my late Grandfather? I think the stone is at least 70 years old. I also think the stone is a barber hone. It look like a slate and is almost black, with deep layers of black in the stone.
When the stone is dry, its grey, bur when its wet it becomes blue/black. The slurry produced by the stone is almost like rubber, and it polls the blade to the surface.
The grid is about 9k, but I need further testing to be sure.
My grandfather lived in Denmark, all his life so the stone could be from Europe. My guess is a german stone, perhaps a Escher stone?
My grandfather died years ago and the stone was hiding in my uncle’s garage. There were another stone as well, a yellow/blue coticule combined. A great stone fore honing!
Does anybody have any ideas for the ID of the stone?

Thanks
Kristian