Removing marble stains?

try ordinary dish soap and very very hot water, and scrubbing with a stiff brush. failing that, try ammonia. failing that, try acetone, but be very careful because acetone is extraordinarily flammable and toxic.

of course, if you like the darker look, you could always rub sunscreen into the rest of the countertop!

stop screwing around with marbles

To get oil up leave fine cat litter on it for a couple of days ( I was told this but it seems a waste of time) or use Palmolive or Dawn dish detergent soap and wipe up a kazillion times. I use a scrub called Bartender’s Friend for almost type of counter or sink. It is packaged just like Comet.I think it may scratch the surface though.