Since mineral surfaces are porous they absorb liquids, which may result in discoloring and staining. Although there are many commercial grade products available on the market which may bring the stone to its to its original luster, taking simple precautions and regular maintenance can save a lot of trouble and cost. All marble and granite tops are sealed immediately after they are installed.
The impregnating substance penetrates the stone clogging most of its pores making its quite impervious to alcohol, juices, soft drinks, cosmetics, cleaners, coffee, food and even oil. With course of time, depending on how heavily the tops are used, the sealer gets washed out. The clear indication of this happening would be the fact that the liquids are easily absorbed into the stone leaving temporary (if promptly wiped off) stains. You should seal your marble every six months and your granite every 12 to 24 months.