The Gemological Characteristics And Color Origin Of Myanmar "Chundaicai" Jadeite

On the basis of literature review,the paper systematically studied mineral composition,chemical composition and spectral characteristics of Myanmar"chun dai cai"jadeite by means of conventional gemological methods,Micro-infrared spectrum,Raman spectrum,X-ray powder diffraction,Electron probe,etc.,and explored origin of its color.Jadeite as main mineral and Myanmar"chun dai cai"jadeite contained a small amount of omphacite,diopside,magnesium albitite,albite,thomsonite and natrolite,barium feldspar,pectolite,nepheline.It's transparency poorer and"cui xing"obvious.Green part were distributed in vein,purple part assumed block distribution.There were a amount of microscopic blastic texture and cataclastic structure commonly.Due to high proportion of jadeite and single mineral composition in purple part,density and hardness of purple part were higher than that of green part.As small radius cationic isomorphism replaced large radius cationic,cell parameter value was slightly lower than standard value.The zoning structure of jadeite was developed.Electron probe showed that nuclear components of the ring belt were belonged to growth environment of high aluminum and high sodium.From inner to outer ring,contents of Ca,Mg,Fe and other elements gradually increased.Sometimes,reactive side metasomatism of pyroxene can be seen,which will indirectly affect light transmittance of sample.Under cathode luminescence,purple part was dominated by blue-purple and orange-red luminescence,and fluorescence color was uniform,indicating environment with low Cr and high Mn.Green part was dominated by yellow-green luminescence,indicating environment with high Mn and little Cr.With increase of Fe content,fluorescence changed from green to yellow.Melting temperature of purple part are higher than that of green part,which indirectly proved that phase transition temperature of pure jadeite is higher,and phase transition temperature will drop when other minerals were doped in jadeite.Spectral characteristics showed that jadeite was composed of Si-O,metal ion and oxygen?M-O?vibration.Combined with differential thermal analysis,it can be proved that nominally anhydrous mineral jadeite contained structural water,but its content was small.It showed absorption peak near 3600cm^-11 in Micro-infrared.By quantitative calculation,green part of structural water had a uniform distribution,while purple part had a trend of less water in the middle and more water on both sides.Pure jadeite appeared colorless and white,and it can be colored by transition metal ions in the M₁ replacing Al ions in jadeite lattice.Green part of"chun dai cai"was colored by Cr³⁺,and then comparing derivative difference between spectral peak at 437nm and 580nm through UV-vis spectrum and its first derivative.It was speculated that influence of forbidden transition of Mn³⁺on color saturation,and it was color formation of purple part.