I would assume it isn't, and seal it. Look for Miracle 511 Impregnator or Stone Tech Impregnator Pro.

The good thing is that you can't "overseal" it -- if you apply sealer, and the stone already well sealed, then at worst none of the sealer will be absorbed and you'll basically just be wiping it back off a few minutes later. Since you'll need to get some sealer to re-apply occasionally in any case, it's not like you're going out of the way to seal it now. And if you haven't sealed marble or granite before, don't let the sound of "sealing your stone" make you think this is a big deal: you spray or wipe it on, let sit, wipe off --it's simple and neither very time consuming nor taxing, especially for something the size of a bathroom vanity.

-- Eric

Thank you both very much for the expert and encouraging information! Bill, I really appreciate all of the time and knowledge you share with us on this forum. I will see which of the two products you mentioned that I can find locally. That is really encouraging that I can't overdo sealing on the marble. I was fearing that I might destroy its beauty if I put more sealer on when there might already be some there.

Additionally, how often should I re-seal the vanity top? I do not mind the upkeep and I would really like to keep the top as unstained as possible (though I expect that at some point in time the top might stain or etch, but I will still love it).

And finally, are there any soaps (hand or clothes) that I should avoid? I generally just purchase some standard liquid hand soap, but I could certainly change if necessary.

I can chime in on soaps, since I have a carrara kitchen countertop. You need a neutral pH soap, definitely not one one with citrus aspects. By any chance do you have a sample of this marble (I am doubting it)? Or maybe you ca get a sample of a similar marble at a tile shop. In any case, do test the soap on it. Put a drip on the marble and let it sit overnight, then wash it off. Tilt the piece in the light and look for etching.

Thank you for the information staceyneil. I will have to see what I can find in terms of pH neutral soaps. I'm not certain if that kind of information tends to be on the bottles. I do not have a sample of the marble, but I might be able to order one. That's a great idea to test out the soaps on a sample.

i've been taught that there are two types of sealers, and one ought not or cannot put one on top of the other. Sort of like water-based and oil-based. The same idea. Is this true? If so, are there any risks with "just sealing it" with the first sealer you buy?

A simple test to check if your marble is sealed is to splash water on it. It should bead on sealed marble.

{{gwi:1410762}}

You can see the water beading on the tile. This shower floor and walls all received 3 coats of a premium sealer.

Not necessarily. Not if it's a breathable sealer (which is actually preferable)