A Study Of Gemological Characteristics And Inclusions Of Spinel From Tajikistan And Myanmar

In recent years,spinel has attracted more and more attention in the jewelry market because of its excellent gemological properties.Myanmar and Tajikistan are two important origins of spinel with high yield and high quality.Most spinel in Chinese market comes from these two producing areas,so it is particularly important to study spinel from these two origins.In this paper,the gemmological characteristics,inclusions,chemical composition and color genesis of spinel from Myanmar and Tajikistan are systematically studied and compared by laser Raman spectroscopy,Microscope,EMPA,fiber optic spectrometer and infrared spectroscopy,and the metallogenic environment of the two areas is preliminarily explored through the characteristics of inclusions.The composition of gem-spinel is mainly MgAl₂O₄.The contents of V,Cr and Zn in Myanmar Spinel are generally high,with the most characteristic of high content of Zn,the trace elements change dramatically.The contents of V,Cr and Zn in Tajikistan spinel are lower than those of Myanmar.Compared with most Myanmar spinel,except blue and part of purple,the content of Fe is relatively high,and the homogeneity of trace elements in each sample is generally higher than that in Myanmar.Cr,V,Fe are the main elements that affect the color of spinel.According to the variety and content,the spinel shows different colors.Sometimes Mn,Co,Zn and other elements are involved.The FWHM of Myanmar spinel Raman spectrum of 407cm^-11 is generally greater than that of Tajikistan spinel,the FWHM of Myanmar spinel is generally higher than 9,and the FWHM of Tajikistan spinel is generally less than 9.There are abundant and characteristic inclusions in spinel.Apatite,carbonate minerals and graphite inclusions occur frequently in both areas.Apatite inclusions in Myanmar spinel often contain black minerals,The echelon octahedral negative crystals are also inclusions with the characteristics of Myanmar.They are epigenetic or pseudosecondary inclusions filled with dolomite,calcite or a mixture of the two components,indicating that Myanmar spinel is of marble type.In addition,pyrite was also found in Myanmar spinel,and 6H-SiC was found for the first time.A large number of zircon inclusions can be found in Tajikistan spinel,and zircon inclusions sometimes exist in apatite inclusions,indicating that the formation of zircon maybe earlier than apatite.In addition,talc was found for the first time in Tajikistan spinel,and massive rutile mineral inclusions are one of the features that distinguish Tajikistan spinel from Myanmar.It is worth noting that magnesite inclusions with CO₂ cavities have been found in both areas,and their specific genesis needs further study.The graphite formation pressure in Tajikistan spinel is estimated to be slightly higher than that in Myanmar based on the raman shift of G-band of graphite inclusions from the two origins.