I have found that using a product called Granite Gold to regularly clean and polish stone & granite surfaces helps to keep the stone’s luster and prevent from pitting which often happens when the surface is exposed to the elements, especially salt air and sun. Another option for regular weekly surface cleaning is with a mixture of dish soap and water, which will need to be mostly water and only a few teaspoons of soap. This can be sprayed on and wiped down with a soft cloth.
Stone countertops such as granite that may loose its luster over time can also be professionally polished using high speed diamond polishing tools. Polishing can be done every six months or depending on the overall condition of your countertops.