Characteristics and Significance of Polytypes and Chemical Compositions of Phengite in Lancang Group, Southwest Yunnan Province
滇西南澜沧群多硅白云母的多型和化学成分特征及其意义

Theoretical and experimental researches and practical observation have all indicated that the celadonite content in the micas obviously increases with the rise of pressure. Therefore, it is considered that phengites formed in multi metamorphism, especially in the multi metamorphism of different metamorphic pressures, must be stamped with the brand of chemical composition. According to the statistical analyses of chemical compositions of 77 samples, there are two generations of phengites in Lancang Group, about 70% of the phengites are the product of high pressure metamorphism, which are consistent with the high and medium pressure metamorphisms of b o values of phengites High and medium pressure metamorphisms are also reflected in the Na Mg figure of phengites. The polytypes of phengites are 3T and 2M 1, and the last is the main polytype.