Do you actually intend carving schist ? It is a metamorphic rock with a pronounced cleavage i.e. like slate, it will split more easily in one direction than in the other.

There are of course small carvings of slate, but anything ambitious could well fall into pieces along the cleavage plane.

I don't recall seeing any tombstones made of schist, though there are some made of slate in North Wales.

Gneiss is another metamorphic rock. It has bands of separate minerals, but less pronounced cleavage than schist. The best definition of gneiss I heard is, "Not gnasty".