Dull spots on marble vanity.

Hi,

I have a question about our bathroom marble vanity (crema marfil).  We
had it installed about 1 year ago.  I soon noticed one or two dull
circles around the sink.  Gradually, more and more dull round spots have
appeared. The largest dull spot is about the size of a quarter, the
smallest spot perhaps a 1/4 inch across. It clearly seems like drops of
something (water?) is causing this, but I have no idea what the culprit
is.  Do you know what types of liquids could be causing this?  And how
do we restore the shine?

By the way, your website is a great resource.

Thanks!

Daniel Young.