Carving slate
 

I've been given some big slabs of slate that i'd love to try to turn
into forest slabs the way Joe Day does with "Muck" to hold the soil in
place.
I have two questions .... #1 what do use to cut this slate into
manageable peices and drill holes ? #2. On a web page, Joe describes
his "Muck" as peat moss and powdered clay ... reminds me of hypertufa.
Where can i find this "powdered clay" stuff?