Ammonium illite that belongs to 2:1 layered silicate minerals is a kind of di-octahedral mica-like clay minerals, and it is the isomorphism of illite, in which the K⁺ was substituted by the NH₄⁺. By means of XRD, IR and XPS, ammonium illite was discovered in some coals and coal partings of Eastern Taihang Piedmont Coalfields, and mineralogical researches were studied in detail. The result of XRD spectrogram shows that ammonium illite's X-ray diffraction peak of d₍₀₀₁₎ is higher than that of ordinary illite, whereas its (002) and (003) diffraction peak intensity is similar. but the ordinary illite's(002)diffraction peak intensity is 24.4%, which is about 1/3 of the (003) diffraction peak intensity. Lattice parameters about ammonium illite in the investigative area are calculated, and the results show that its space group is C2/m, with every parameters including a (0.52133nm to 0.52774nm), b (0.89814nm to 0.91693nm), c (1.02538nm to 1.05285nm), β(101.127° to 101.699°), z (2, volume is 0.47611nm³ to 0.49224nm³), density (2545 e^-/nm³ to 2697e^-/nm³). The above descriptions indicate that the ammonium illite is 1M polytype. The results of IR spectrogram demonstrated that the deformation vibration peak of NH₄⁺ range from 1427.58cm^-1 to 1431.95cm^-1, and the N 1s XPS banding energy of NH₄⁺ is 402.4eV. In nature the ammonium illite-illite solid solution is more general than pure ammonium illite. Thus, mostly ammonium illite contains a certain amount of K. Therefore, the K 2p peak is often observed by the XPS spectra.