Identification Characteristic of Turquoise Associated Mineral Crandallite-Goyazite

Abstract

Recently, a kind of turquoise associated mineral has appeared on the market, which is very similar to turquoise in appearance. The authors studied a relevant sample by means of conventional gemmological tests and the other methods including thin-section observation, electron probe analysis, X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy and ultraviolet-visible analysis, etc.The results showed that the main mineral component of the sample is crandallite and goyazite, as well as a certain amount of turquoise, etc. The main colour of the sample is blue, partially bluish green, and the blue colour is uneven, mainly enriched as dots or lumps. It has cryptocrystalline texture with the density of 2.52 g/cm3, and its refractive index is about 1.62 (point measurement). The infrared spectra of crandallite-goyazite show the main absorption peaks at 3 585, 3 420, 3 140, 1 320, 1 116, 1 039 cm-1 and 604 cm-1, and the Raman spectra of crandallite-goyazite show the main peaks at 1 104, 1 034, 987, 612, 518, 257 cm-1 and 185 cm-1, which are different from those of turquoise. Since it is difficult to identify this kind of turquoise associated mineral, conventional gemmological tests, Fourier infrared spectrometer, Raman spectrometer, X-ray powder diffraction analysis and electron probe analysis should be ultilized comprehensively.