Mistery mottled schist

[Matheus]

Wandering through the wilderness I found a small wooden combined travel case (razor case + hone + strop) very cheap. The poor thing was very dirty, with some dings and crusts of whatever, and its little hone marred with deep scratches overall.


I could't resist and took the little poor thing home.
Today I spent some time trying to get it cleaned but gave up, took it completely apart and spent a lot of elbow grease sanding the old lacquering out and lapping the hone.

The stone revealed itself very beautiful, a kind of schist or slate, somewhat grayish and mottled with darker inclusions. Tastes muddy, smells fresh, very hydroscopic, less hard than my chinese 12k and its slurry have a latte appearance. What kind of hone can be this?