Kaolinite, dickite and nacrite are polytypes of the kaolinite family, in which kaolinite is quite common while nacrite is very rare in nature. As is well known, different kaolinite polytypes occur in different gelogical environ- ments. Nacrite usually appears in an environment with relatively high tem- perature and pressure. Therefore, it is of great significance in theory and practice to distinguish kaolinite polytypes in detail. Characteristics of the kaolinite family from the Early Carboniferous Fang- jiashan kaolin deposit were studied by means of X-ray diffraction, infrared spectroscopy and potassium acetate intercalation. With the entrainer of K-acetate acted on the kaolin, an intercalated compound with a 14.0A spa- cing appeared. After it was replaced by water, a characteristic 8.35A base spacing of nacrite hydrate intercalate was formed. Under the condition of normal atmosphere, the nacrite hydrate was stable. However, when the nacrite hydrate was placed in an atmosphere with saturated ethylene glycol, the nac- rite hydrate was destroyed rapidly. This demonstrates that Fangjiashan kao- lin is a nacrite-bearing kaolin deposit. Further"n.ore, IR and intercalation technique also show that the aacrite mineral exists in a form of coarser fraction larger than 2 um and the domain of kaolinite decreases with the increase in that of nacrite. This may indicate that nacrite was formed thro- ugh reconstruction of kaolinite under geological structural stress. The nacrite- bearing kaolin deposit is only seen, in the vicinity of the Jiangshan-Shao- xing deep fault, along the transitional zone of two geological units, suggesting that the movement of the Jiangshan-Shaoxing deep fault might have con- tinued to the Hercynian period or even to the Yanshanian period. It is the compression and compresso-shearing of the fault that provided the pressure for the formation of nacrite in this area.