The Study About The Gemological And Mineralogical Characteristics Of Hanzhong Serpentine Jade With Different Colors

Hanzhong serpentine jade is found in Hanzhong,Shaanxi Micang Mountain.The jade from the mines in this area includes serpentine jade,diopside jade,tremolite jade and mica jade.This article mainly takes the serpentine jade in this area as the research object.This article intends to systematically study the gemological and mineralogical characteristics of Hanzhong serpentine jade.In order to explore the similarities,differences and internal reasons of those different colors jade,this article has conduct the research by fieldwork,gemological experiment,polarizing microscope,XRF,EPMA,infrared spectroscopy,Raman and UV-Vis spectrum.Hanzhong serpentine jade mainly has five color series:bright yellow,brown-yellow,brown,yellow-brown and dark brown.The bright yellow jade is serpentinized marble,the brown-yellow,brown,yellow-brown,and dark brown varieties are serpentine jade.Gemological tests show that the serpentine jade RI is 1.55～1.56;the Mohs hardness is 3～4;the bright yellow and dark brown jade samples’relative density are slightly higher than other colors.The bright yellow may because of the calcite,and the dark brown is affected by the higher Fe content.The main microstructures of Hanzhong serpentine jade are microscopic cryptocrystalline metamorphic structure,microscopic scale-like metamorphic structure,metasomatic grid structure.Dark brown Hanzhong serpentine jade is formed by diopside,other colors Hanzhong serpentine jade is formed by carbonate minerals.According to the electronic probe test,in the serpentine of Hanzhong serpentine jade,the Mg O content is 40.60%～44.61%,the average value is 42.72%,which is mostly lower than its theoretical value 43.64%;the Si O2 content is 39.61%～43.78%,the average value is 42.72%,which is mostly lower than its theoretical value of 43.36%.It can be seen that the isomorphic substitution are both in Mg-O octahedron and Si-O tetrahedron of serpentine.Two strong peaks near 3700cm^-1 and 3683cm^-1 and a weak peak at 3651cm^-1 can be seen in the Raman spectrum.Compare and identifie the wavenumber,position and shape of the peaks in this interval,it can be known as serpentine.As for the infrared spectrum,in addition to the peaks of lizardite,the brown-yellow and yellow-brown samples can also see absorption shoulders near1020 cm^-1 and 470 cm^-1,which may contain some chrysotile.The UV-Vis spectrum of Hanzhong serpentine jade has 366,385,434,462,665,723nm bands.The 365～460nm band is mainly caused by the d-d transition of Fe³⁺,and the 625～729nm band is caused by the charge-transfer transition of Fe²⁺-Fe³⁺.The quantity and intensity of the bands in the365～450nm range are more and higher than the bands in the 625～729nm,so Hanzhong serpentine jade present a yellow-dominated hue.EPMA and XRF show that the Mn O content of brown-yellow,brown,yellow-brown and dark brown Hanzhong serpentine jade are generally higher than bright yellow samples,while its brown is affected by Mn²⁺.Hanzhong serpentine jade deposit is a regional metamorphic-contact metasomatic type deposit.The original magnesium carbonate rocks were regionally metamorphosed into dolomitic marble,which was further metamorphosed by contact metasomatism due to bedding intrusion of basic magma and further metamorphosed to form the serpentine jade deposit.