Gemmological and Mineralogical Characteristics of Changhua Yellow Stone

Changhua yellow stone is produced in Changhua, Zhejiang Province. Its appearance is very similar to Tianhuang, and the gemmological and mineralogical study of Changhua yellow stone is of great significance to identify Tianhuang, especially its origin scientifically. In this paper the authors used microscope and polarizing microscope, X-ray powder diffractometer (XRD), infrared absorption spectrometer (FTIR) and scanning electron microscope (SEM) to study the microscopic characteristics, primary and secondary mineral components, and the fracture micro appearance characteristics of the rough stone crust and compared with the stone's internal XRD and FTIR characteristics. The results showed that the external mineral components of most Changhua yellow stones are mixed minerals of dickite and kaolinite in a low degree of order, and several samples are composed of pure dickite of lower degree order. Meanwhile, the internal mineral components of the stones are similar to the external, nevertheless, the content of kaolinite is higher, and there is little difference in the degree of order. The chemical composition of the main constituent minerals of the external and interior of Changhua yellow stone can be obtained by quantitative analysis of energy spectrum. There are many kinds of secondary minerals that are mostly distributed in the white pits on the crust of the Changhua yellow stone, including hematite, svanbergite, quartz, dolomite and gypsum etc. The distribution morphology was observed by EDS energy spectrum test.For the micro appearance characteristics, the diameter of kaolinite mineral particles constituting the crust of the stone is about 5 μm, and the gap between dickite particles is unclear. The particle boundary is smooth, and the aggregates are arranged in book shape, while the crystallization degree of the internal of the stone is good, which is stacked in pseudo-hexagonal sheet or imbricate shape.