I printed off a bunch of info on the Tidy Cats Crystals for the vet today. Just in case it will help. The Tidy Cat's web page & Nestle page weren't very helpful as far as the ingredients but I did find this:

Household Products Database

I took her all that info. Not sure if the litter IS for sure the culprit, but I'm just trying to do my part to help.

By the way, we are doing a full litter change this weekend. No more crystals in this house. Did I already mention that?