Gemmological Characteristic of Gobi Nephrite from Southern Xinjiang, China

Gobi nephrite is a significant type of nephrite. After weathering, exfoliation and transportation processing, the original deposit mines were carried to the Gobi Desert, and the surface of Gobi nephrite was uneven with intense greasy luster through long-term weathering. The major producing regions are in southern Xinjiang.36 pieces of Gobi nephrite samples from southern Xinjiang were chosen as research objects. Conventional testing, LA-ICP-MS, FTIR spectrum and Raman spectrum were applied to obtain gemmology, mineralogy and spectroscope characteristics.From the relative test results, LA-ICP-MS tests showed that the main chemical compositions of Gobi nephrite were SiO₂, MgO and CaO. The content of SiO₂ was 57.6%-59.6%, MgO was 23.4%-25.2% and CaO was 13.9%-15.1%, which were basically consistent with the theoretical content of tremolite. The microscopic characteristics on the surface of Gobi nephrite observed by the high resolution digital image technique showed that the surface of Gobi nephrite presented a distinctively uneven and undulating appearance.Impurity minerals were often deposited in weathering pits and fissures. Infrared spectra displayed the typical tremolite absorption between 900-1 150 cm^-1 and 400-760 cm^-1. Raman spectra demonstrated peaks at 3 672, 1 061, 1 030, 932, 675, 530, 417, 395, 372, 225, 179, 123 cm^-1, which is in accordance with mountainous nephrite.