You should be able to have a competent repair or restoration specialist from a reputable granite or marble fabrication shop come to your home and fix the problem. If it is a very small chip (less than an eighth of an inch around, my first try would be super glue. Keep in mind the fill will be fairly clear in color, which may match the dark specks, if not use an indelible marker after you smooth the glue to color it black. Use the gel type super glue if it is on a vertical portion of the sink, otherwise use a thinner variety. Clean the chip with sop and water, let it dry then use rubbing alcohol to remove any grease or oil residue. Use a masking type tape to isolate the chip so you have less work once the glue dries. Fill the chip and once the glue is dry, use a single edge razor (Use extreme caution, razors are by nature sharp) to gently scrape, not cut the glue flush to the sink surface. The manufacturers of these sinks claims they are difficult to scratch, but pay attention to your pressure or you might create scratches on the sink itself. Hold the blade perpendicular to the surface of the sink and take your time scraping the dried glue down changing to a fresh blade often. If the chip is in a radius area of the sink, you will have to be a bit more creative and probably use steel wool to remove the excess dried glue. I would start with #000 and see how that works, maybe using #00 to start the process and finish with #000 or #0000 steel wool to match the finish of your sink. If your chip is larger than an eighth of an inch around, I would recommend hiring a repair and restoration specialist from a competent granite fabrication shop to make a color matched epoxy to fill the blemish.
If you have any questions, feel free to contact me, Brandon Wiese -
[email protected] - http://www.StoneRepairman.com