Characteristics of Zircon gems related to Basalt in the Southeastern Vietnam

Tóm tắt

This paper presented the on gem–quality zircon found in the southeast, Vietnam which related Cenozoic alkaline basalt and deposited on hillsides or stream beds as placers. Zircon samples in this area is mainly brown, orange, gray and colorless; transparent and diamond luster. In addition, they mostly have the effect of changing color under different lights and often have the shape of 4-sided cylinders, typical of the tetragonal crystal type. The standard gemological characteristics such as refractive index, specific gravity, absorption spectrum, optic characteristic and ultraviolet fluorescence (long wave and short wave) confirmed the studied samples belonged to the zircon mineral group. Notably, the refractive index could not be measured by the refractometer and the high specific gravity (from 4.66 to 4.71) indicating that this belonged to a high zircon. The X-ray diffraction analysis determined a tetragonal crystallization and with the chemical formula ZrSiO4. The Raman spectrum with peaks at 226, 352, 438, 972 and 1004 cm-1 and the FTIR spectrum with peaks at 448, 607 and 898 cm-1 showed that the studied zircon was radioactive. The HfO2 content and Ti− thermometer showed that the studied zircon originated from the molten syenite with the crystallized temperature of 829.78−869.04°C. The result showed that the basalt in the southeastern Vietnam, an area of more than 1.000 km2 with the depths varying from 1 to more than 100 m, weathered crust from 1 m to more than 30 m, would be a potential source of gem–quality zircon for jewelry gemstone.