Had that table been sealed previously? If it is indeed black granite it most likely should not be sealed and that may be why you are getting rings. Water does not stain. If it were a porous granite it will darken it but would dry out. I would try some acetone on a small section to see if the issue is due to it being sealed.

Hi Vin Marks! we have never sealed it but I had assumed it came sealed because it was so shiny. We were told it was granite when we bought it (it is very heavy!) Agreed there have been spills/rings on here from things other than water. that big spill sat all night.

That is etching from acidic water, on marble.

Ah! Ok. That makes more sense than granite. I didn't ask enough questions when we bought it regarding care, etc. My fault fo sure. That makes more sense than granite. I didn't ask enough questions about care, etc., when we bought it. It's my fault, for sure! Do you know how to get rid of these marks? I suppose it needs to be sealed since it's marble.?

It can be refinished, but that's not usually a DIYer job. Schedule a MORE Anti-Etch treatment immediately after it's refinished please.