Hi, Sean. A special colored epoxy is used to glue repair marble. This is available at stores that supply architectural stone or that make grave markers. Color matching is important and the stone is polished with diamond papers to level the repair and even the shine. At the least, you want to take a sample of the marble with you when you buy the glue. Ideally, you should have a pro do this because the abrasives are very expensive and a perfect job will cost you less in the long run.