Abstract: The coal member CP₂ of Daqing Mountain coalfield,and has more than 40 beds of tonsteins at most.There are illite of illite-kaolinite clayrocds(or tonsteins) at the seam roof or in the tonsteins near the top of coal member being in scour contact with the conglomerate member CP₃,and,downwards,are all kaolinite clayrocks(tonsteins) in both the seam and seam floor.The kaolinites have in different degree been alterad into tobelites and diaspores.The former were distributed along the joint fissures of the tonsteins in the shape of scaly and fibrous aggregates,ribbon of the pseudomorph of the kaolinite crystal grains.The latter occurred in the banding with rich organic matter taking the form of the microcrystalline or fine-crystalline aggregates.The features as above show that kaolinite in the clayrocks and tonsteins was trasformed into illite on open condition which K⁺ ions can be got or trasformed into tobelite on enclosed condition.The NH₄⁺ ions can stem form deep underground.