There are different high gloss tile & concrete sealers available which will probably give you the look you're wanting although (from what I understand) you will have to reapply it every few years.

I was given a tip years ago to use Thompson's Water Sealer on stone things, as it brings up the color really good.
But it also needs to be reapplied every few years, depending on weather. Our Phoenix sun can be pretty hard on things during the summer, I try to keep as much GJ in shade as possible.

hugs, Karen