Gemmological and Mineralogical Characteristics of Idocrase Jade from Hanzhong, Shanxi Province

Idocrase, also known as "California jade", is a variety of precious jade that has been appeared in the market in recent years. Its density and appearance are very similar to those of jadeite, and idocrase is mostly sold as jadeite product. The gemmological characteristics, mineral components and spectral characteristics of the samples collected from Liuba County, Hanzhong City, Shanxi Province, were studied by conventional gemmological tests and advanced instruments including polarizing microscope observation, X-ray powder diffraction analysis, infrared spectroscopy, Raman spectroscopy and X-ray fluorescence spectroscopy. The conventional gemmological testing results showed that the relative density of the idocrase samples range from 3.29 to 3.47 and most of the colour is green or yellowish green, and emerald green clump can be seen in some samples. XRD testing results showed that the main constituent mineral of idocrase from Hanzhong is idocrase, containing a small amount of grossularite, diopside and chlorite. The infrared spectra show that the characteristic peak in the fingerprint area of idocrase is mainly located between 1 200 to 400 cm^-1, among which the absorption peak of 1 200 to 800 cm^-1 belongs to the stretching vibration of Si-O-Si and O-Si-O, while the absorption peak under 600 cm^-1 is caused by the bending vibration of Si-O and the stretching vibration of M-O.Microscopic Raman spectral showed that there are 11-13 characteristic Raman peaks in the range of 100 to 4 000 cm^-1 in idocrase samples. Besides idocrase, the samples also include diopside, chlorite and grossularite. XRF analysis showed that the emerald green clump of idocrase contains a small amount of Cr and V compared with the matrix, and it is speculated that the emerald green is caused by these two elements.