The black stuff that u referring to its called mica and its a one of minerals you will find in lots of granite. Mica is very flaky and crumbles. people will call and say that while cleaning they counter they notice black specs on white paper towels, because that stuff washes off and comes out off the stone. Its also very soft and almost impossible to polish. That's the reason most of the time that u have pitting in granite and depending on how big the mica minerals are you may have little pits or gouges. The only way to fix it is to fill it with clear epoxy or ca glue. But the customer needs to know that its the beauty of nature nothing else.