Crystals of Clear Choice Cat Litter is the true evolution of cat litter, providing unprecedented convenience and performance. Each silica crystal granule contains millions of micro-pores that act like tiny sponges, quickly absorbing and trapping odor-causing particles. Odor control is quick and effective. After a few exposures to moisture, the color of the indicator crystals fades. It's time to replace the litter when all of the Indicator Crystals have faded.