The Study On Gemology And Mineralogy Of Agate In Yanyuan County,Sichuan Province

Yanyuan agate is a new variety agate recently discovered in Yanyuan County,Liangshan Prefecture,Sichuan Province.Local people named Yanyuan agate "colourful jade".The green/yellow and pink/purple colours are the most abundant.The microstructure of Yanyuan agate was observed through the use of infrared spectroscopy,raman spectroscopy,x-ray powder diffraction and ultraviolet-visible spectroscopy.It is the structure of the material that determines its colour.The results show that Yanyuan agate is unique and rich in colour,whereas Shanxi agate is usually dark,white/gray and purple.The agate is translucent,with a refractive index of 1.54.The relative density range of Yanyuan agate is 2.56 g / cm3 to 2.63 g / cm3 compared to Shanxi agate at 2.64 g /cm3 to 2.66 g / cm3.The density of Yanyuan agate and Shanxi agate is between 6 and 7.It is thought that the yellow-green of Yanyuan agate is the primary colour,whereas red is the secondary colours found along the hull.Yanyuan and Shanxi agate are mainly aphanitic and non-fibrous in structure.Under the polarized microscope,it was observed that Yanyuan agate granule is very fine.It was difficult to find impurities.The presence of hematite/magnetite was observed in a small number of samples near the exterior.Shanxi agate quartz particles were found to be fine.Larger impurity particles were discovered in the green part of the observed chlorite,as well as other parts of the pyrite,calcite and sericite.FTIR and x-ray diffraction results show that the main minerals of Yanyuan agate are ?-quartz.In the infrared reflection pattern of Yanyuan agate within the two absorption bands of 1179 cm-1 ± and 1110 cm-1 ±,the absorption band width and the peak shape were smooth,indicating that the crystallinity was poor at 800 cm-1.Calcite and other minerals were found in the ferrite of the Yanyuan agate,and the impurities of calcite and chlorite were detected in the Shanxi agate.Raman spectroscopy further confirmed that the red ?-quartz Yanyuan agate contained impurities hematite,goethite and iron ore.The results of UV-Vis spectra showed that there was a strong absorption peak at 540 nm in the pink / purple samples,and all the blue-violet regions were absorbed.Within the green/yellow samples at 520nm-580 nm there were different degrees of absorption and the blue-violet area was all or at least in part absorbed.Through the colour measurement,we can quantify Yanyuan agate hue,saturation and brightness – allowing us to evaluate its quality.