New unknown hone

I was shown pictures of old hone which so far i failed to id. Any thoughts?
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Šarplaninski kamen

I've never seen one before today, interesting stone and for what I can read from german label says Snake honestone, special fine-fine.

It's a Bohemian :D

And one of the possible locations of origin is somewhere in Toscany. I will see if I can get my mits on it just to have a feel and direct sight. From pics it looks like one of the old Moravian slates which were mined long time ago.