Application of Infrared Spectroscopy and Raman Spectroscopy on Identification of Heat-treated Aquamarine

Experiments show that yellow-green beryls can be transformed into aquamarines by using appropriate heat treatment.However,in jewelry market,the price of natural aquamarine is quite different from that of heat-treated aquamarine.Thus exploring diagnostic identification characteristics of heat-treated aquamarine is of great importance.Previous identifications of heat-treated aquamarine were their internal inclusion characteristics,which were observed through microscope.However,it was difficult to identify flawless aquamarines.The authors selected some samples from Altay to treat under a reducing atmosphere at different temperatures for 3hours.Fourier transform infrared spectrometer and Raman spectroscopy were used to explore the characteristic absorption peaks of the heat-treated samples.The results show when the heating temperature is above 400℃,the peak caused by the stretching vibration of[Fe₂(OH)₄]²⁺ at 3 233cm^-1 is significantly reduced or even disappeared and the sharp absorption peak around 5 268cm^-1 caused by H₂O becomes wide and gentle.The relative intensity of absorption peak at 8 700and 6 818cm^-1 caused by H₂O weakens as the heating temperature is elevated.It is found that the Raman spectral intensity at 682and 3 604cm^-1caused by stretching vibration of Si-O-Si reduce as the heating temperature rises,and spectral intensity at 1 070cm^-1 decreases.After heat treatment at 700℃,the baseline of Raman spectrum drifts upward obviously.