Clean the chipped area with an ammonia-based cleaner and a soft cloth. Allow the area to dry.
Fill in the chipped area with a layer of fast-drying glue. Allow the glue to dry overnight. Fill in the area again with another layer of glue. Continue to add layers until the chip is completely filled -- slightly above the countertop's surface level. Allow the glue to dry thoroughly.
Cut off the top layer of the glue by holding a sharp razor blade at a 45-degree angle to the surface.
Sand the area with fine-grit sandpaper to remove any bumps.
Buff the area with a soft cloth and a quartz polishing cream, to restore the original brilliance of the countertop.