Gemmological Characteristics And Colorimetry Study Of Dandong Yellow Colored Quartzite Jade

The research object of this paper is yellow colored quartzite jade from Dandong,Liaoning Province,also known as“Dandong yellow chrismatite”.Since its appearance,there has been few studies on it.In order to understand its mineral composition and spectral characteristics,on the basis of conventional gemmological parameters testing,the quartzite jade produced in Dandong area was researched by means of micro Raman spectroscopy,infrared spectroscopy,UV-vis spectroscopy,X-ray powder diffraction spectroscopy?XRD?and X-ray fluorescence spectroscopy.Aiming at the“whitening phenomenon”,a dehydration experiment were designed,with a scanning electron microscope.To explore the effect of“H₂O”on its color,three elements was used to quantify its color change.Through the observation of the characteristics under the microscope,it can be concluded that the main mineral of the yellow quartzite jade in Dandong is quartz,a small amount of red mineral particles and trace phengites,which has an obvious crystal structure.Raman spectroscopy shows that the main component of Dandong Yellow quartzite jade is?-quartz,followed by iron oxides such as hematite,goethite and so on.The half-height width of 464cm^-11 peak shows a positive correlation with the content of moganite calculated using the model in a certain range.The 400cm^-11 peak is widely present in the samples.The splitting peaks at 800cm^-11 and 1080cm^-11 peak are related to the crystalinity.The infrared spectrum shows that only vibration absorption peak of Si-O-Si appears.The degree of splitting of 800cm^-11 and the intensity at 543cm^-11 decrease when the moganite content increase.In addition,XRD shows that the samples have high crystallinity,which is between coarse quartz and artificial crystal.The X-ray fluorescence spectrum shows that the main chemical composition of yellow quartzite jade in Dandong is not only SiO₂,but also Fe,S,Ca,K and Al.Its color is related to Fe element.The UV-Vis spectrum shows a weak absorption peak of hematite.The SEM shows that its grain size is relatively large,and should be named“quartzite”,and its color caused by the infiltration of iron minerals in the later period.During the dehydration process,the chromogenic elements of the samples did not change in valence state.The three values of color were used to quantify the color.When dehydrated at 100?-200?,the absorbed water was lost,and its L*value and h°value remained basically unchanged,and the C*value decreased.The color of the naked eyes becomes lighter.When dehydrating at 250?-300?,the coloring mineral goethite loses its structrue water,the L*value,the h°value,and the C*value all decrease.The yellow part of the samples become reddish.When dehydrating at 350?-450?,the structure water?Si-OH?was lost,the L*value and h°value remained basically unchanged,and the C*value decreases slightly,and the color of the naked eyes becomes lighter.