Colouration in purple jadeite-jade from Myanmar:A spectroscopy and chromaticity investigation
55 Myanmar purple jadeite-jades samples were comprehensively analyzed by electron microprobe analysis(EMPA),energy-dispersive X-ray fluorescence(ED-XRF)spectroscopy,Fourier transform infrared(FTIR)spec-troscopy,ultraviolet-visible(UV-VIS)spectroscopy and colorimetric methods.The results show that the main chemical compositions of Myanmar purple jadeite-jades are SiO2,Al2O3 and Na2O,and the contents are close to those of standard jadeite.Chromaticity test analysis showed that the chroma C*of purple jadeite-jade is mainly con-trolled by the colour coordinate a*,while the hue h° is mainly controlled by the colour coordinate b*.Myanmar purple jadeite-jades can be classified into two types:Type Ⅰ show the main absorption bands at 570 nm which is assigned by chromophore Mn3+and Type Ⅱ with two main absorptions at 540 nm and 610 nm are colored by charge transfer between Fe2+-Ti4+.The absorption peaks of Fe3+existed in both types of Myanmar purple jadeite-jades,and the full iron content in the samples determined their hue and lightness.
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