add pure fluix to macerator for fluix dust recipe

Not directly feasible since it would allow for duping. You can get around it by crafting the pure crystals into block form (which takes 8 pure crystals), then crafting it back into crystal form (which gives 4 regular crystals). This can then be macerated and doesn’t allow you to infinitely dupe pure crystals.

That's exactly right. Allowing for maceration of pure quartz crystals into a full dust would introduce a dupe loop. I don't think people would particularly want a recipe that makes two small piles (one half of a full dust) from pure crystals, but that would be the only way to balance it.

As Rhapsody notes, you can downgrade pure crystals into half as many regular crystals via the block recipe.

Could probably go somewhere in between and add a maceration recipe for fluix blocks -> 4 fluix dust, if it doesn't exist already.

I don't recall a recipe for macerating the blocks of AE2 crystals, but I'm kinda disinclined to add new ones since you can turn the blocks into the base quartz which already can be macerated.

It's already a bit exploity that you can get crystals in this manner; if were to adjust the recipes for them I'd remove turning pure crystals back into base crystals via blocks and just have maceration recipes for the dust.

maybe add a contentTweaker item "Pure Fluix Dust"? or something along those lines, that way one can still use pure fluix for such recipes without introducing a duping problem
but that may take more effort than it's worth

Adding a new item would require a lot of recipe adjustments to make it interchangeable with the regular fluix dust. It would be very much overcomplicated compared to macerating to half of a dust each, let alone the existing system where you can do what you need with no changes at all.