Its a form of granite. The drywall guys put puddy and paint over top of the gray cement board. Problem is mortar doesn't stick to that smooth surface so we had to do what is called a scratch coat around the edge. You take a 1/8" thick metal mesh, nail/screw/anchor it into the wall and apply a thin layer of mortar, allow it to dry and now you have a surface the mortar will stick to when you apply the stone.
The wall we built with cement block and then covered it. If you notice the wall is a little funky at the column and we're going back on Monday to redo it. We'll turn the stone out so that it matches up with the other side (against the column).......little communication error with what the customer was wanting but we'll take care of it. Carpet went down the day after we went.......charcoal.