Gentlemen!

Anybody knows something about the stone?

The factory says on their website only the followings: (link)

Sharpening stone - Marttiini


Traditional sharpening stone of the Lappish serizite quartzite.
The sharpening stone has two surfaces of different grit grades: first the blade is sharpened with circular movements on the rougher side, after which the blade edge is finished on the finer side by removing the circular marks. The sharpener also includes a groove for sharpening hooks.

I asked the factory and some dealers some questions but they did not answer. So knows anybody something about the stone?

It’s a natural stone or man-made?
If natural, is it naturally two sided or glued ?
Grit sizes (about) ?

Thank you in advance:
K.