Gemmological Characteristic of "Yongchuliao" Feicui (Jade) from Guatemala

In recent years, a new variety of Feicui (also translated as jade) named "Yongchuliao" has emerged in Chinese markets. This kind of Feicui with a dark green colour is from Guatemala. In this study, the authors collected 4 pieces of "Yongchuliao" products and 1 piece of rough stone. The conventional gemmological characteristics, chemical composition, spectral characteristics, and colour origin of the "Yongchuliao" samples have been tested, analyzed and discussed through infrared absorption spectra, laser Raman spectra, UV-Vis spectra, and electron probe micro-analysis, respectively. The results showed that the refractive index of "Yongchuliao" samples falls between 1.66-1.67 (point measurement), with a specific gravity of 3.33-3.34, presenting a glass luster and inert fluorescence under both long wave and short wave ultraviolet light. Infrared spectra revealed that the main mineral of the "Yongchuliao" samples are omphacite, and the composition of omphacite has remarkable consistency. Raman spectra showed that the crystal structure of this type of omphacite is P2/n, and other phases in "Yongchuliao" samples include titanite and amorphous carbon. Moreover, titanite often has a "reticulated cross" section. UV-Vis spectra exhibited characteristic peaks at 437 nm (caused by Fe³⁺), and 636, 658, 688 nm (caused by Cr³⁺). And the colour of "Yongchuliao" under natural light is primarily influenced by Cr³⁺ and is also affected by both Fe²⁺ and the charge transfer between Fe²⁺ and Fe³⁺. The average chemical formula of "Yongchuliao" according to the results of electron probe micro-analysis is (Na_0.50Ca_0.49)_0.99(Mg_0.46Fe_0.08Al_0.48Cr_0.01)_1.03. In addition, "Yongchuliao" is richer in Mg and poorer in Fe. A higher content of Cr makes it distinguishable from Guatemalan Mocui. "Yongchuliao" with only titanite as its accessory mineral is also different from Mocui from Myanmar and Guatemala.