The image to the upper left is a classic example of mistreating your stone. Using polishing compounds from the neighborhood  hardware store, this top was severely stained within the first year. The image to the upper right is the end result of an extraction  which removed the stain, followed by impregnation (should be done every six months) to prevent future stains.

The image to the upper left shows a common problem that could have easily been prevented by the plumber. The upper right image is the end result of  a poultice extraction  followed by a silicone sealer around the fixture to stop the moisture from staining the stone.