Oh, Heather, I am so sorry to hear this --- R.I.P. Darcy.
I've just researched quartz (to see if it has some nutritional value or might be listed in the ingredients list under a chemical name other than silicon dioxide), to no avail. My guess is that you're right about it accidentally ending up in the Nutriphase.
I imagine we would all like to hear how Petsmart responds and what you want to do about the situation. This appears to be similar to finding shards of glass in dog/cat food!
Hugs to you, Heather.