Escher stone

[nicknov]

I have an old Escher stone 8"x1 3/4" x 3/4" a few small slivers around the edges have started to come away I have made a box for it and have never dropped it One such sliver measures 3/4" x 1/32"
It seems to delaminate of flake of. I dont want to keep lapping to a flat portion in case it encourages more pieces to do so. I try to avoid using that area. Has enyone experience of this is this common if so can I prevent this happening, is it just inherent of this stone or could it just be a flaw. I understand it is a sedimentary rock and perhaps some of the layers have not bonded when it was formed. Anyone have experience of this happening to them or ideas why it is happening