Hi, I have a dark green granite countertop in the bathroom. one area
has developed a ring of some kind of deposit (whitish). I believe it
is water mark or caused by the hard deposits in the water. It is where
I put the cups.

How do I clean those out? It's not very severe but noticible. If I
wipe it with a damp cloth it disappears. but after the water dries it
appears again.

Thanks.