Hi Maurizio,
I'm so happy I found your site. I am care taking a house in Mexico where they put in these lovely so called granite counter tops. I have since been told that they are marble. They were never sealed on the job site and I do not believe they were sealed before as they started spotting immediately. I was told by the installers to be very careful with lime. Go figure the owners put in counter tops in a country that uses lime quite a lot.  Unfortunatley, no matter how careful you are limes squirt and you don't always see where the squirt went to until after the fact. The owners have even left ring marks from glasses sitting on the counter for only a couple of hours. I have read some of your forums and this counter does not seem to have grooves from etching just the white marks from the spills and lots of water marks from the water around the sink. Can you please send me any info you have and tell me what products to get to help prevent this problem in the future. Thank you very much for your time and expertise.
Sherri