Thank you for ur response. Perhaps this might be of interest to some of your members.
I love trying working with new materials and branching out from wood working such as welding and in this case stone. To answer your question the stone I used is a slate which is VERY hard . . . don't know the hardness scale . . . but I went through 5 diamond disks cutting and shaping the stone mosaic.
I also bought an air driven wet polisher for stone around 250.00. . . It is much like any 5 " angle grinder BUT THIS ONE FEEDS WATER CONTINUOUSLY TO WHERE YOUR WORK IS. . . . 4