ROUND Crystal Litter is SPECIFICALLY DESIGNED FOR AUTOMATIC LITTERBOXES and tray refills. ROUND CRYSTALS ROLL ON HARD SURFACES. CONSIDER A LITTER MAT AROUND THE LITTERBOX. Round lasts longer than Chunk or Sand style. It is made from silica sand (SiO²). Through processing, this sand is converted into crystals that contain millions of microscopic pores which exhale moisture from cat urine. This process also kills bacteria. THIS ADVANCED TECHNOLOGY PROVIDES THE GREATEST ODOR CONTROL OF ANY LITTER. The crystals also pull moisture from the droppings, which further minimizes odor. Crystal litter is rapidly becoming the favorite among those with smaller living quarters, such as townhomes and apartments, because of its very superior odor control.