Clear Choice Crystals Cat Litter is truly the evolution of cat litter, offering a level of convenience and performance never before available. Millions of micro-pores in each silica crystal granule act like tiny sponges, quickly absorbing and trapping odour-causing particles. Odour control is fast and complete. Indicator Crystals fade in colour after a few exposures to moisture. When all the Indicator Crystals are faded, its time to replace the litter.