Bentonite is clay, so named for its first location, Fort Benton in Wyoming (USA). Here this is called swelling clay or fuller's earth. It is a sodium - clay, with particles that are so small that they can make the soil waterproof. One kg of bentonite can hold 10 kg of water. It can improve sandy soil for agricultural purposes.
It is used as a filling for the (cat) litter. The material absorbs the urine and forms a hard lump which can be scooped from the box.
Bentonite is also used to clear wine, among other things to precipitate proteins.

Each mill has its own character and is worth at least one book. It is impossible to describe all the techniques, materials, transfers and constructions. They are each personalized and optimized for the specific application at a specific location.