How to Clean Hard Water Marks from Black Granite

I have read the advice to many different folks on these forums--a wonderful set of pages.  In one answer, Maurice tells one questioner that the white water marks left by hard water on a granite counter top are probably on the surface and so can be cleaned.  That's what I have--what appears to be the white residue of hard water on the black "granite" (which, I understand, is probably not really granite) counter top.  The counter top is not purely black, but appears marbled with gray and bluish chunks mixed in (I'm afraid I am not sure what kind of counter top it is, as it was here when we moved in).  There was no mention, however, of HOW to clean the water stains.  Does anyone know how I can clean these white hard water marks off the stone?  I've done an internet search, and I'm not keen on using a razor blade.  Here are some other options I've seen suggested: trisodium phosphate, Pledge with orange oil, marble polish, glass cook top cleaner, and Bar Keeper's Friend.  I'm afraid to use any of these, however, without some more expert advice.