Mineral Component and Genesis of High-Grade Green Jadeite Jade from Guatemala

High-grade green jadeite jade samples from Guatemala were selected as the research objects. Gem microscope, polarizing microscope, microscopic laser Raman spectrometer and electron probe microanalyser, etc., were used to carry out the analysis on the appearance characteristics, magnification observation, constituent minerals, microstructures, Raman spectra, mineral chemical compositions of the samples. According to the constituent minerals and their evolution, 3 periods of mineralization were observed: The product of early mineralization period is jadeite with coarse-grained, hypautomorphic-automorphic granular-columnar texture, and their chemical compositions are very pure; The main mineralization period is metasomatism, in which the product formed in the earlier period is fine-grained jadeite with relatively higher content of FeO, Cr₂O₃, MgO and CaO than that of jadeite formed in early mineralization period, and the product formed in the later period is fine-grained omphacite which contains high content of MgO and CaO, the shades of green of which vary correspondingly to regular variations of Cr₂O₃ content; The products of late mineralization period are jadeite (or albite) + titanite, etc. in filling texture, where titanite is mainly distributed in reticulated veins between jadeite/omphacite particles or in microfractures. The combination of jadeite (or albite) + titanite + fluid inclusions formed in the late period, which appear as the white cotton-like substance in the jadeite jade, is actually a type of fluid-melt inclusions. The fluid phase in the fluid-melt inclusions contains CO₂ and CO etc., and the 2 145 cm^-1 characteristic Raman shift peak is the strongest, indicating a h ighly reductive forming environment with high CO content, which is corroborated by the amorphous carbon generally observable in the samples. Jadeite is the main mineral or one of the main minerals in most of the high-grade Guatemalan green jadeite jade samples studied. In high-grade green jadeite jades, the late period combination of jadeite + reticulated titanite + CO-dominated fluid inclusions commonly found in the white "cotton", can be used as an important reference feature to distinguish Guatemalan high-grade green jadeite jades from Burmese green jadeite jades.