The illite is a mineral of the class 9 silicates, according to the classification of Strunz, of the Group of Muscovites. It is a not expansive, micaceous clay. The illite is a phyllosilicate or silicate laminar.Structurally the illite is quite similar to the Muscovite or sericite with more silicon, magnesium, iron, and water; and slightly less aluminum tetrahedrico and potassium interlaminar.The chemical formula is (K, H3O ) (Al, Mg, Fe ) 2 (Yes, ) 4O10 [( OH ) 2, (]H2O )][1], but there are also considerable ion substitution. It occurs as aggregates of small monoclinic crystals grey to white. Due to its small size, accurate identification usually requires x-ray diffraction analysis. The illite is a product of the alteration or weathering of the Muscovite and feldspar in weathering hydric and thermal environment. It is common in sediments, soils, clayey sedimentary rock, and metamorphic rock. It differs from the glauconite in sediments by x-ray X.La analysis illite was described in Maquoketa in Calhoun County, Illinois, USA, in 1937.