Locality determination of inky black omphacite jades from Myanmar and Guatemala by nondestructive analysis

Abstract

Locality identification of high‐quality inky black omphacite jades (inky jades) from Myanmar and Guatemala is becoming increasingly urgent. In this study, Raman, Fourier transform infrared (FTIR), and energy‐dispersive X‐ray fluorescence spectroscopy (EDXRF) were performed to distinguish samples of inky jade from the two localities. The Raman spectra revealed the presence of several types of minor minerals in Guatemalan samples, including titanite, albite, orthoclase, taramite, celsian, and cymrite, whereas the Myanmar samples consisted almost entirely of omphacite. Taramite and lath‐like celsian occurred only in Guatemalan samples and had significance in locality tracing. The Raman and FTIR reflectance spectra of omphacite shifted to low wavenumbers in proportional to isomorphic substitution Na+Al3+ → Ca2+(Mg2+, Fe2+). Semiquantitative calculations based on the Raman (~680 cm−1) and IR modes (~658, ~576, and ~424 cm−1) showed consistent jadeite end‐member components (~43% to ~64%) in the Myanmar samples, whereas those (~23% to ~87.5%) of the Guatemalan samples were wider and generally lower. In addition, the full width at half maximum values (FWHMs) of Raman shifts near 680 cm−1 in the Myanmar samples (avg. 15.03 cm−1) were less than those (avg. 16.81 cm−1) of the Guatemalan specimens. Linear discriminant analysis (LDA) based on Raman spectroscopy identified most samples with accuracy of 85.5%. Combined with results by EDXRF, these analyses revealed the characteristics of a relatively narrow range of Na+Al3+ → Ca2+Mg2+ isomorphism for the Myanmar jades and a more developed Na+Al3+ → Ca2+(Mg2+, Fe2+) isomorphism for the Guatemalan jades. This study might have implications for commercial applications, archeological research, and judicial expertise.

Comparative Evaluation of Chemical Garden Growth Techniques

“…The bands located at 280 and 440 cm –1 can be assigned to Mg (OH) 2 . In addition, the band at 690 cm –1 was attributed to the Si–O chemical bond. , It was clear that the intensities of these bands showed notable differences between structures, which were due to the different orientations and compositions of the samples. This result indicated that the structure produced in the membrane experiment had more Mg and O content, which was consistent with the EDS analysis.…”

Color-Causing Mechanisms of Guatemala Jadeite Jade: Constraints from Spectroscopy and Chemical Compositions

“…The Raman and FTIR spectra of the omphacite shift proportionally toward the low-wave number with the isomorphic substitution of Na + Al 3+ → Ca 2+ (Mg 2+ , Fe 2+ ). Semi-quantitative calculations based on the Raman (~680 cm −1 ) and FTIR modes (~658, ~576, and ~424 cm −1 ) showed consistent jadeite end-member components (~43% to ~64%) in the Myanmar samples; whereas, those (~23% to ~87.5%) of the Guatemala samples were wider and generally lower [9,10]. The rarity of jadeite and its top color are the main factors in evaluating jadeite.…”