Characterization of a rarely encountered sericite with earthy luster

Abstract

A rarely encountered sericite was investigated using X-ray diffraction, differential thermal analysis, and scanning electron microscopy. XRD analysis shows that the pattern of the sericite in the sample is similar to that of illite. DTA (TG) analyses show that only a weak heat absorption reaction takes place at 566°C, which is contributed to the polymorphic transformation of quartz, and no change in mass was detected in the range from ambient temperature to 800°C. These reveal that no water escapes from the crystal structure of the clay mineral during heating and therefore indicated that the clay mineral is obviously sericite in species instead of illite. SEM observations show that the sericite particles are significantly small in size and growth steps and irregular structures develop on the crystal surfaces as well as the colored mineral inclusions, which might suggest some loss of optical properties of the sample and thus lead to the variance, with earthy luster of the aggregate, from typical sericite in optical characters.

Keywords

clay mineral / sericite / illite / luster / X-ray diffraction / differential thermal analysis / scanning electron microscope

References

[1] Berry L G, Mason B, Dietrich R V. Mineralogy, 1983, San Francisco: W. H. Freeman and Company. 430-443.

[2] Guoxi Chen, Yueming Zhang. The Handbook of Phase Transformation Patterns of Minerals by DTA and XRD, 1989, Chengdu: Sichuang Science and Technique Publish House. 126-186. (in Chinese)

[3] Pu Wang, Zhaolu Pan, Lingbao Weng. Detailed Mineralogy (medium volume), 1984, Beijing: Geology Publishing House. 429-450. (in Chinese)

[4] Zbik M, Smart R St C. Nanomorphology of Kaolinites: Comparative SEM and AFM Studies. Clays and Clay Minerals, 1998, 46(2): 153-160.