if you still have the chip you can epoxy it in place, if not you can still use epoxy to build it back up... not much else to do in that case.
When installers put granite etc. type counter tops together they adhere them and seam them with colored epoxy, I would go to a very good custom tile/countertop store and ask them if they have any you could buy.
you won't find it at home depot or any place like that though.