Quartizite counter tops while, very hard, even more so then granite can be porous. We do recommend a Water Penetrating sealer such as Bullet Proof by Stone tech. A water penetrating sealer will create a bond in the stone that will last about 7-10 years. Where a silicone sealer will need to be reapplied every 6 months to a year. A silicone sealer will not penetrate deep enough into the quartizite to protect it. Now your countertops SHOULD come sealed if not sealed once installed in the home. IF your countertops have already been sealed with a silicone sealer you will have to have that removed (which can be a hard job to diy) before adding a water penetrating sealer.