Rocky cat litter is a type of clumping cat litter that forms hard clumps. It can be made from natural rock formations like moler, or from clay. 
Ingredients
Moler
A natural rock formation found in Denmark, moler is made of clay and diatomaceous earth. The diatomaceous earth gives moler its unique absorption qualities. 
Clay
Clay is crushed, dried, and then crushed again to make traditional clay litter. Bentonite clay is added to make clumping clay litter. 
Benefits
Odor control: Rocky cat litter can absorb liquids and odors, and can help inhibit bacterial growth. 
Lightweight: Rocky cat litter can be lighter than traditional clay litters. 
Easy to scoop: Rocky cat litter forms hard clumps that are easy to scoop. 
Other cat litters
SmartCat Lightweight Clumping Litter: A lightweight litter that forms hard clumps and is 99% dust free 
Arm & Hammer Clump & Seal Platinum Multi-Cat Complete Odor: A clumping litter that can control odors for up to 14 days 
ARM & HAMMER Traditional Cat Litter: A litter made with odor absorbing clay and baking soda that neutralizes litter box odor