Names aren't a guarantee. Test the slabs. Quartzite won't be scratched by a piece of glass tile. Marble easily will show the scratch. A little lemon or vinegar will get a reaction from marble. Nothing from quartzite. Always test. No matter what. And do the layout with no cuts until you approve. Plus inspect before it leaves the shop. Check the seam match and no edge chips.

Yes to the test for sure. Just ask for the samples to test .

Who cares about names? They get made up all the time by marketers. Marble is still marble, not quartzite. Full all of it’s natural beauty, and all of it’s ability to scratch, chip, etch, and stain.

Test for geological type, and see if you can live with it.

Also watch out for the slabs that pass the glass scratch test, but are still porous. Those need to be sealed regularly.

Thanks, everyone, I would definitely test any "iffy" slab I was planning to purchase. I guess my real question is---yes, considering that these sellers label things quartzite that are actually marble---without running to every slab yard and testing each one, is it even possible that there is a quartzite that looks just like the cristalita azul marble? Or are they all marble, including cristallo blue/azul?

Anything is possible but like life there are zero absolutes. I would test whatever I chose, period. If you do not test, you lose the right to be upset later when it is marble and you do not like it. Unfortunately as mentioned several times, anyone can call a stone anything they like. Caveat Emptor.