..artificial "gemstone" it's second only to diamond in hardness and cuts faster then natural stones.As a bonus it's cheaper than diamond hones and the size of the grit particles can be controlled very consistently.M2 is my fave between M2 and D2 but I have nothing against D2(BM806D2!! 
)-which is quite similar to M2 like but technically less tough/more brittle. 
)-which is quite similar to M2 like but technically less tough/more brittle.