I'm not a tile expert by any means, but I have done some lapidary work as a hobby. If the stone is soft enough, you may have better luck with just sanding the edges to get the soft rounded edge. I did that with several marble strips I used as shelves in my oversized niche with great results. Three sanding blocks, medium, fine and very fine, and a bit of elbow grease. It took me about 40 minutes to round off and smooth the edges of 6' of marble shelves, then an impregnating sealer. I could have used my dremel or angle grinder, but I was worried the soft stone wouldn't sand down consistently with a power tool, so opted for manual sanding that I could better gauge the pressure applied. Just an option...

They CAN be mitered but you need to be carefull with it. First, you want to do the mitering on a wet saw. Second, you don't want to miter all the way to the edge of the face of the tile. Leave a shy 1/16- 1/32" of "meat" to the edge. If you try and cut a sharp miter, the edge will come out extremely ragged.