Well if it's quartzite you're in good shape since quartzite is harder than granite. Some super whites are marble and mislabeled as quartzite, and some are actually quartzite.

I need to take back the etching comment...it did etch, but just not as obviously as marble. Oddly, it didn't change the sheen so much as it "discolored" the stone slightly. White marble was much more obvious when it etched.

It's very hard to say as there is no consistency in naming stones. Super white is sometimes a slightly different kind of marble. Dolomite, I think? Which does take longer to etch, but still etches. Your tests are the best prediction of how the stone will perform.

Your results are perfectly consistent with most Superwhites. It's dolomitic marble with a little bit of quartz in it. Dolomitic marble etches, but more slowly/subtly than regular marble. And because there is a bit of quartz here and there, it will scratch glass sometimes but not always.

The reason some people report zero etching is because of labeling/mislabeling.

Hope that helps! And good for you for being so thorough!

It does-thanks! This forum has been unbelievably helpful...can't imagine all the things I'd never even know to question without the help of this online community.