I also got this from Nature's Variety ingredient glossary:

Montmorillonite is a clay that is primarily colloidal silicate, which contains over 50 ultra-trace mineral compounds including Antimony, Barium, Beryllium, Boron, Bromine, Cadmium, Carbon, Cerium, Cesium, Chloride, Chromium, Cobalt, Copper, Dysprosium, Fluoride, Gadolinium, Gallium, Germanium, Iodine, Lanthanum, Lithium, Manganese, Neodymium, Nickel, Phosphorus, Rhenium, Rubidium, Samarium, Scandium, Silicon, Silver, Strontium, Sulfur, Tellurium, Thallium, Thorium, Tin, Titanium, Vanadium, Ytterbium, Yttrium, Zinc, and Zirconium. Feed studies by the Veterinary Medical Diagnostics Laboratory at Texas A&M University have shown that Montmorillonite clays can sequester (bind) aflatoxins contained in grains and oilseeds.