Thanks for your advice; I had the same problem now. I will try quartzite grit RHS; I hope it will be ok. To tell the truth, I didn't know that granite can be used for these purposes. Indeed, it is a rather ancient material that has shown its best side for many millennia. It is actually used in many industries because it is very durable. Some years ago, I ordered for our kitchen such a countertop http://countertopshq.com/dallas-white-granite/. Indeed, I remained satisfied because it doesn't absorb dyes, is shockproof, and withstands high temperatures. This is one of the most practical materials