I can't answer your questions, but I love the tile!

Why don't you ask your tile supplier and/or your tile installer?

We have an onyx backsplash & weren't aware of any grout issues. Our backsplash is sealed but I don't know what with.

I have onyx in my kitchen floor, bathroom floor, media room floor, and bathroom shower (all as accents). The material is soft so it does scratch easily,. but it is not porous! I have tried to stain it and it did not. I used aquamix gold sealer but even the sealer just wipes off (meaning the material does not absorb any sealer).

I used mapei keraset with keraply (white thinset) to set the onyx and there was no staining. No presealing.

It is a gorgeous stone!

I'm leaning toward onyx too. These pictures are both terrific.

Someone here uses food grade wax (beeswax?) every six months on her honey onyx, if I remember correctly. Otherwise, hers tends to whiten up.

So, will sealing the tile before grouting prevent the tile from picking up stain from the dark grout? If so, what sealer would you recommend?

If you're going to use a dark grout, it probably wouldn't be a bad idea. As for the sealer to use as a grout release, my favorite would be Aquamix's WATER based penetrating sealer. I can't explain it, but the water based sealers work better as a grout release, even though the solvent based sealers work better to protect the tile long term, and yes, you can use one after the other. I would suggest you use them both from the same manufacturer, in which case, you'd want the Sealers Choice 15 to seal it after grouting.

Now, that all said, one other thing you might think about, instead of using a black grout, it'll help alot with pigmentation and possible staining if you were to step it down just a hair and use a charcoal grout, instead.

Sorry-- that's Sealers Choice GOLD 15.

How did it turn out? I'm doing some similiar.