Granite countertops are relatively easy to take care of, and such preventive maintenance as cleaning up spills quickly and avoiding setting hot pots on them will keep the surface in good repair. Properly installed granite countertops are not likely to crack, but if they do, there are steps you can take to repair them. Serious cracks and chips should be repaired by a professional.
Clean the surface around the crack thoroughly with acetone or a 50-50 mixture of household ammonia and warm water. Dry thoroughly. Don't use a product that will damage the finish on the granite.
Mix granite epoxy according to the manufacturer's directions. Mix only enough hardener and resin to use in 10 or 15 minutes.
Use the color pigment kit to add color to the epoxy, again following the manufacturer's instructions.
Spread epoxy in the crack with a small tool, such as an artist's palette knife or a foam brush. Use a toothpick in very small cracks. Quickly wipe up any messes because once the epoxy hardens it will be very difficult to remove.
Seal the crack in the granite with granite sealer. Apply the sealer, let it set for 10 to 15 minutes, then apply another coat. Let the crack repair cure for a day.