Crystal Chemistry of Green Jadeite Jade from Myanmar

Abstract

Jadeite jade is a Na-Al pyroxene mineral that is a single chain silicate. The objectives of this study are to explain cause of color in green jadeite jade from Myanmar, to clearly understand the mineralogical properties and crystal chemistry of green jadeite and to study the green jadeite jade structure in term of relationship between color and spectroscopy. The 38 jadeite jade samples from Myanmar were separated on the basis of their colors into 5 groups including light bluish green, bluish green, light green, green and yellowish green or greenish yellow. Mineralogical properties of jadeite jade from Myanmar have the specific gravity (S.G.) ranging from 3.20-3.41 (3.34 on average), the refractive index (R.I.) varying from 1.652-1.670 with birefringence of 0.008-0.010. The mineralogical properties and FTIR result of the samples are determined as natural jadeite jade. From FTIR result, samples found importantly absorption bands that are 3000-3500 cm-1. The band at 3000-3500 cm-1 is assigned to OH stretching mode. From resulting of Electron Probe Micro-analysis (EPMA), Ultraviolet-Visible-Near Infrared absorption spectroscopy and X-ray absorption spectroscopy, jadeite structure consists of Fe2+ and Fe3+. The simultaneous presence of Fe3+ and Fe2+ means intervalence charge transfer. In some samples, samples present Cr3+ and trace elements that are chromophores as Mn, Co, V and Ti in absorption board band at 600-700 nm. Fe and Cr in jadeite structure showed absorption spectrum at 370, 380, 420 nm and broad bands at 600-700 and 900-1000 nm. Then, cause of green color occurs Fe2+-Fe3+ intervalence charge transfer (IVCT) and Cr that substituted ion in M1 (octahedral oxygen coordination). Therefore, cause of green color in samples occurs from Fe, Cr and trace elements as Co, V and Ti that occupied in M1 sites, octahedral oxygen coordination in jadeite structure. Paler color groups showed lower absorbance than darker color groups. In darker color groups, Fe and Cr found in jadeite structure more than paler color. Fe and Cr increased in jadeite that is darker green color.