Study on Gemological Characteristics of Blue Sapphires from Baw-Mar Mine, Mogok, Myanmar

Abstract

This paper employs an X-ray powder crystal diffractometer (XRD), an X-ray fluorescence spectrometer (XRF), an ultraviolet-visible-near infrared spectrometer (UV-Vis-NIR), a Fourier infrared spectrometer (FTIR), and a laser Raman spectrometer to systematically investigate the gemological characteristics of blue sapphires from Baw-mar mine, Mogok, Myanmar. The results show that the FTIR spectra and UV-Vis-NIR spectra of the sapphire from this mine are significantly different from those of sapphires from other origins, which can be used to identify sapphires from this mine. The main crystal structure of the mineral sapphire from Baw-mar mine is corundum. The predominant chemical elements are Al and O, and the color-causing elements are Fe, Ti, V, and Ni. The characteristic ultraviolet absorption peak appears at 418 nm, which is mainly caused by the d-d transition of V3+ ions. The intensity change of the 946 nm ultraviolet absorption peak indicates that the presence of Ni2+ ions may aggravate the gray tone of sapphire and reduces its transparency. Compared with sapphires from other origins, sapphires from this mine have three characteristic infrared peaks of kaolinite at 930, 1025, and 1110 cm−1, of which the single peak at 930 cm−1 is attributed to -OH translation, and the double peaks at 1025 and 1110 cm−1 are attributed to the Si-O stretching vibration. The peaks at 369, 410, 437, 565, 633, and 739 cm−1 in the Raman spectra are attributed to [AlO6] octahedron vibration. Our work provides insight into detailed spectroscopy data of blue sapphires from this mine and the identification of sapphires from different origins through spectroscopic characteristics.

Keywords

• sapphire
• gemological characteristics
• spectroscopy
• Baw-mar mine
• Myanmar