Like rock salt
Pros:
excellent odour control, even when poo is not covered; minimal tracking.
Cons: uneconomical, as it obviously doesn't clump, so you end up shovelling a lot of yellow pee crystals into the waste, which is very heavy, again uneconomical and unsustainable; the crystals stop absorbing when full so pee trickles through to the tray floor; the crystals are large and sharp and hurt cats' paws so they get out of there as fast as possible, leaving uncovered poo; expensive.
Won't use this again.