My husband, John, found the black boulder that he used for this fountain at a local quarry. At first he thought it was granite, but it turns out to be slate.
Basically, he just did a bit of carving to level the top so the water would come out evenly and he polished the surface to a nice shine. Most important, he had a hole for the bubbling water bored down the length of the rock by a guy who has the right tools. (This fellow makes garden lighting for the landscape trade out of carved granite stones that he imports from China, and he has drill press machines that do the job.)
The stone is set on top of a large plastic basin that serves as a water reservior and holds a submersible pump. It's covered with screen and fine pea gravel. It looks simple, but John had a few setbacks. His first plastic basin was too small, and the pump he's bought wasn't powerful enough either. Once those problems were solved, the bubbling fountain worked beautifully. As anyone who has done these kinds of projects knows, putting a fountain like this together is never as easy as the magazine articles make it look.