Comparison of Spectral Characteristic and Chemical Compostion of Barite, Diaspore and Calcite Mixture Imitated Turquoise and Natural Turquoise

By Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray fluorescence energy spectrometer and UV-Vis spectroscopy, a new kind of turquoise imitation and natural turquoise were studied comparatively. The results show that this kind of imitation is mainly made of mixtures of barite, gibbsite, calcite and organic matter. Its appearance are very similar to natural turquoise. The imitation and natural turquoise can be distinguished according to the following identification criteria: the Raman spectra and infrared spectra of the imitation show the characteristic peaks of barite, gibbsite, calcite and organic matter, and there are no natural minerals such as quartz and graphite in the imitation's black patterns. The chemical compositions of the imitation are mainly BaO, Al₂O₃, SO₂ and CaO, without the key chemical composition P₂O₅ of natural turquoise. The UV-Vis-NIR absorption spectra of the imitation show absorption of 675 nm, without absorption at 427 nm and absorption in the near-infrared light region.