Gemstone Mineralogical and Spectroscopic Characteristics of
Quartzose Jade (“Mianlv Yu”)
YU Lian-gang1, LIU Xian-yu2*, CHEN Quan-li3
1. Dehong Teachers' College, Dehong 678400, China
2. College of Jewelry, Shanghai Jian Qiao University, Shanghai 201306, China
3. Gemmological Institute, China University of Geosciences(Wuhan), Wuhan 430074, China
Abstract：In recent years, a new kind of quartzose jade named “Mianlv Yu” from Myanmar has emerged in the west Yunnan jewelry market. It is characterized by delicate texture, and green color with different blue and yellow tones, and some green are similar to high-quality Australian green chalcedony. However, the color origin of this jade is still unclear, and there is still a lack of relevant theoretical support for its species identification, quality evaluation, and market promotion. In this paper, the mineral composition and structure, chemical constituent, spectral characteristics, and color origin of this jade were studied using an Infrared spectrometer, Raman spectrometer, UV-vis spectrometer, X-ray fluorescence spectrometer, X-ray powder diffractometer, and Polarizing microscope. The results show that the main mineral is α-quartz (containing trace Moganite), mainly cryptocrystalline, and a small amount of microcrystalline, accounting for more than 90% of the content, followed by sericite and willemsite in the form of microgranular and scaly, and extremely trace amounts of nepouite and chromceladonite. Occasionally, there is secondary disseminated iron clay in the local position, and the whole structure is microgranular with scales. The infrared transmission spectrum mainly shows the infrared absorption characteristics of α-quartz, Infrared absorption peaks at 1 019, 800～600, and 462 cm-1 are attributed to the anti-symmetric stretching vibration of νas(Si—O), and the symmetric stretching vibration of νs(Si—O—Si) and the bending vibration of δ(Si—O), respectively. The characteristic absorption peaks at 3 463, 1 639, and 1 399 cm-1 are caused by the anti-symmetric stretching vibration νas(H—O—H) and bending vibration δ(H—O—H) of free water molecules between quartz microvoids. In the Raman spectrum test, except for the Raman group peaks 204, 262, 355, 395, and 463 cm-1 indicated the characteristics of α-quartz, the weak Raman peak at 501 cm-1 indicated the presence of trace Moganite, and the Raman peak at 675 cm-1 indicated the presence of willemsite. The chemical composition and ultraviolet-visible spectra characteristics show that the jade contains trace impurity elements such as Mg, Al, Cl, K, Ca, Ti, Cr, Fe, Ni, Ni, and Fe are the main chromogenic elements. This jade's significant difference in Ni and Fe content reveals why it presents two different color series: green to bluish green and greenish yellow to yellowish green. The high content of Ni and low content of Fe produces green to bluish green series, and the change of blue tone is positively correlated with the content of Ni. The same degree of low content of Ni and Fe produces greenish yellow to yellowish green series, and the change of yellow tone is negatively correlated with the content of Fe and Ni. In conclusion, the mineral species of “Mianlv Yu” is green chalcedony, and its color characteristics should be attributed to impurity minerals such as willemsite, sericite, and secondary iron argillaceous. Nickel exists in the forms of free Ni ions and impurity mineral willemsite. Willemsite is a rare mineral in other sources of green chalcedony, which should be considered an important reference feature for origin traceability. This study has enriched the data of green chalcedony's varieties and its origin information, and also provided essential data for further exploring the metallogenic geological background of “Mianlv Yu” Jade.
Key words：“Mianlv Yu” Jade; Quartzose; Mineral constituent; Spectral characteristics; Color origin
