Most facetable black diamonds are industrials. They're a maze of fractures and alternating growth directions, and pieces tend to fall off during cutting. Because of the alternating crystal growth, cutters also encounter different directions of hardnesses on the same facet. "When you're talking about black diamond, it's really a conglomerate," says natural colored diamond dealer Alan Bronstein. "The more you cut, the more little things keep falling off the stone." Nizam Peters, director of the American Institute of Diamond Cutting Inc. in Deerfield Beach, Fla., says there are two rules of thumb when cutting black diamond. "If the stone has a good orderly arrangement of growth, there will be only a little resistance, since there are still carbon inclusions, but normally it will be straightforward cutting. However, most black diamond has a great deal of resistance. They are highly knotted