Vermiculite, (Mg, Ca, Na) m (H 2O) n {(Mg, Fe, Al) 3[(Si, Al) 4O 10](OH) 2}( m = 0.3–0.45), is mainly a 2:1-type (TOT-type) trioctahedral layer-structured magnesium silicate that is rich in interlayer exchangeable cations and can expand upon ignition. It gets its name because the product after ignition-induced expansion resembles a leech. In the classification of mineral crystal chemistry, it belongs to the silicate class, the layer-structured silicate subclass, the montmorillonite-vermiculite group, and the vermiculite subgroup. In the structural-functional classification of mineral raw materials in mineral material science, vermiculite belongs to the category of two-dimensional structural minerals and the subcategory of functional minerals.