Abstract
Mineralogical data of sericite found near the Yoji pass, Ozawa-mura, Kanragun, Gumma Prefecture, are reported in this paper. The material is white powder with silky luster and occurs as a hydrothermal alteration product of quartz-diorite. Specfic gravity is 2.87 The result of the chemical analysis is SiO2 47.65, TiO2 0.10, Al2O3 37.03, Fe2O3 0.01, FeO tr., MnO tr., MgO 0.04, CaO tr., K2O 9.02, Na2O 0.76 H2O(+) 4.97, H2O(-) 0.73, P2O5 0.02, total 100.33%, and this gives the structural formula of (Na0•09K0•76)Al2•00(Al0•87Si3•13)O10(OH)2• The d. t. a. curve shows two endothermic peaks at 635°C. and 980°C.. X-ray studies of a pre-heated specimen revealed that the final destruction of the sericite lattice occurs at about 970° to 1, 000°C., mullite appears at 1, 000°C. and, that at 1, 100°C. sericite is completely transformed into mullite. The (060) spacing is 1.501Å., which indicates that the specimen is of the dioctahedral type.
Although the sericite leached by hot concentrated sulphuric acid displays X-ray powder lines different from those of original specimen, the results of acid treatment confirmed that the sericite is more durable than chlorite to acid attack.
