Gemmological-mineralogical Features and Forming Conditions of Staurolite, Kyanite and Sillimanite from North of Shanxi Province

Staurolite, kyanite and sillimanite are widely distributed through the metamorphic layers in the north of Shanxi Province and their distribution presents a certain regularity from the north to the south, namely from Jianshan to Hejialan. In order to find out the forming conditions of the three minerals and further reveal their indicative significance to the metamorphic degree of the rocks involved and the interrelation between metamorphic degree and the fault of Xichuan River, EPMA and geothermometer are adopted in the research. The results of the estimated calculations, along with the petrologic features, indicate that staurolite and kyanite in the north of Xichuan River are formed at the higher pressure p=(5~7)×10⁸Pa and the lower temperature (t=520~550℃), whereas sillimanite in the south is formed at the higher temperature (t=570~600℃) and the lower pressure (p<3×10⁸Pa). It is concluded that the regular distribution and forming conditions of staurolite, kyanite and sillimanite are closely related to the fault of Xichuan River.