Calcium sand encourages the animal to eat it to obtain their calcium requirements.
In sufficient quantities, calcium can "denature" the stomach acid, rendering itself (and everything else in the gut) completely indigestible. This is what can cause impaction.
I personally won't use any sand-based substrate for any animal that *does not live on loose dunes sand* in the wild.
"My bum has been a bum for a very long time, but that does n't mean I have to listen to what it says."
- Terry Pratchett, Fifth Elephant