Gemological And Mineralogical Study Of Jadeite From Nammaw,Myanmar

The Nammaw jade deposit in Myanmar is located in the Pakant jade mining area and is the largest primary jade ore body discovered so far.8 samples were selected from the center of the ore body to the surrounding rock of the Nammaw jade deposit in Myanmar;visual and microscopic observations,conventional gemological tests,mineral phase and chemical composition analysis(X-ray powder crystal diffraction analysis and electronic Probe analysis)and spectroscopy analysis(infrared spectroscopy and Raman spectroscopy)were conducted,to reveal the mineral composition,structural structure,chemical composition and spectroscopy characteristics of Myanmar Nammaw jade,deepen the understanding of the Myanmar Nammaw jade deposit,and at the same time provide a basis for the discussion of the genesis of jade and the development of new uses.The main findings are as follows:From the ore center to the surrounding rock,the composition Nammaw jade ore body in Myanmar is in sequence white zeolitized medium-coarse jadeite,white zeolitized fine-grained jadeite,off-white strongly zeolitized fine-grained jadeite,and chromite-kosmochlor-magnesioriebeckite rock,phlogopite schist,dark gray-green serpentinite(the original rock is peridotite),glaucophane epidote chlorite schist.Through routine gemological tests on eight samples,it is found that the relative density of all samples is lower than that of the national standard of jadeite.But since the main minerals of G1 and G2 are jadeite,and the secondary minerals are zeolite group minerals,etc,they are refered to as Myanmar Nammaw jade in this article based on the understanding of colleagues in Myanmar;it is actually a kind of jade in a broad sense,though the relative density does not conform to international regulations so it does not belong to jadeite in the strict or narrow sense.The main minerals of samples G3-G8 are not jadeite,so they are called surrounding rocks.G3 is strongly zeoliticized jadeite rock,the main minerals are zeolite group minerals,and the secondary minerals are jadeite and tobermorite;The main mineral of G4 is magnesioriebeckite,and the secondary minerals are chromite and chromian jadeite;The main mineral of G5 is phlogopite,and the secondary minerals are pyroxene,chromite,and kosmochlor;The main minerals of G6 and G7 are antigorite,and the secondary minerals are chromite;the main minerals of G8 are chlorite,epidote,and glaucophane,and the secondary minerals are sphene and muscovite.Through mineralogical study on eight samples,it is found that the structure of Myanmar Nammaw jadeite is mostly fragmented and filled.Through mineralogical study on eight samples,it is found that Myanmar Nammaw jadeite is mostly a fragmented and filled structure.The content of jadeite from the center to the edge of the ore body is getting lower and lower,and the particle size is getting finer and finer;the content of zeolites around the jadeite grains or between the cracks are getting higher and higher.After studying the mineral composition of Myanmar Nammaw jadeite and the chemical composition of the minerals by X-ray powder crystal diffraction experiment and electron probe experiment,it was confirmed that the main minerals of Myanmar Nammaw jadeite are jadeite and zeolite minerals.The mineral composition of the surrounding rocks is complex,but the presence of phlogopite,glaucophane,etc.indicates that Burma's Nammaw jade was formed in an ultra-basic environment with low temperature and high pressure.In the process of testing the surrounding rock,the existence of the combination of chromite,kosmochlor,and chromium-containing amphibole was observed.This combination provided an important source of Cr for the formation of Myanmar green jadeite.On the jadeite grains,zonal structure is observed,which was formed because of the difference in the content of Mg and Fe.In addition,fluid melt inclusions have been observed in jadeite and magnesia amphibole.The characteristics of the zonal structure and fluid melt inclusions indicate that minerals such as jadeite crystallized from fluid melt systems rather than a result of hydrothermal metasomatic alteration.At the same time,combined with the analysis of the phase diagram,it can be seen that the pressure of Nammaw jade in the formation stage of jadeite is higher than about 6-7.5GPa,while the pressure in the later formation stage of analcime is lower than this approximate range.Burma's Nammaw jade and its adjacent surrounding rocks contain a large amount of zeolite.The central part of the ore body is dominated by analcime,and the types of zeolite increase to the edge.The existence of a large amount of zeolite provides a basis for the development of new uses of jadeite and jadeite zeolite in this area.