Gemmological Characteristic and Colour Origin of Purple Anthophyllite Jade from Xinjiang, China

A kind of rare and high price purple anthophyllite jade which is similar to nephrite in appearance and texture found in Xinjiang nephrite market was studied. According to conventional gemmological tests, the refractive index of the purple anthophyllite jade is 1.61 (point measurement), the relative density is 3.00, and the fluorescence response under UV lamp is inert. The comprehensive analysis of X-ray powder diffractometer, Fourier transform infrared spectroscopy, polarizied microscope and Raman spectroscopy tests showed that the main mineral component of the anthophyllite jade sample is anthophyllite with fibrous distribution. The purple part of the sample contains a small amount of clinochlore, while the pink part does not contain clinochlore. Further comprehensive analysis by micro-UV-Vis spectrometer, energy dispersive X-ray fluorescence spectrometer, SEM scanning electron microscope and EDS spectrometer showed that the colour of the pink part of the anthophyllite jade sample is caused by the anthophyllite containing Fe and Mn elements, while the colour of the purple part is caused by the combined action of the amphibolite containing Fe and Mn elements and the clinochlore containing Cr element. There is a positive correlation between the saturation of purple colour and the content of clinochlore.