I think you'd better find out for sure just what kind of material you are dealing with before you riun them trying to clean marble when they're not. If you take one to someone who deals in marble they should be able to tell you. It could be limestone too.

I`m recommended you use Liquid silicone

Here is a link that might be useful: Seattle cleaning service

It looks like real marble to me. Try this first. Take mild dish soap (Ivory)dilute in a spray bottle. Wet the stone well and then do a light scrubbing with a nylon bristle brush. The yellowing likely will NOT be removed by regular cleaning as it will likely need the application of a "poultice" to "draw" the stain out of the pores of the stone crystals. If it lightens with light cleaning it may make you happy but other wise cleaning with a cleanser that can float the contamination up and out and this time WITHOUT detergents. If you would like the name or other methods on the poultice let me know
Stan

Thanks for the advice. Would love to know what the poultice recipe is. tx!

sherriz - they are "whiting" (finely ground chalk mixed with water) and spread on wet. Klet it dry and brush it off.

Other recipes can be found: google for marble poultice and seewhat comes up.

Stan, I'd like to know more about poultices for removing stains from marble. My local marble/granite dealer had no advice to offer.

Dixie_Woman, there was a discussion over on Kitchens in the last few days about stains on a marble kitchen counter, with some suggestions about different poultices. Maybe there will be something in there to help?

Here is a link that might be useful: stains on a marble kitchen counter