Raman Spectroscopic Study on Inclusion in Sapphire from Azad-Kashmir

Initially, sapphire from Kashmir only refers to the sapphire from Kashmir valley located in "Jammu and Kashmir". But recently, the locality has been expanded to encompass some neighboring areas, such as Azad-Kashmir controlled by Pakistan. However, there is a significant price difference between the classical Kashmir sapphire and other Kashmir sapphires. Therefore, it became essential to identify the specific origin of Kashmir sapphire.The inclusions and spectral characteristics of blue and purple sapphires from Azad-Kashmir were studied by micro-Raman spectrometer in this study. The test results show that the blue and purple sapphires bear similar inclusions, and they both contain zircon and graphite mineral inclusions. The typical inclusions are gas-liquids associated with graphite inclusion, as well as zircon, and graphite composite inclusion. Distinct blue-purple parallel angular bands and growth striations are observed. In addition, tube-like inclusions are found in blue sapphires. Hematite and diaspore crystal inclusions are found in purple samples. All the mineral inclusions mentioned above are identified by the micro-Raman spectrum. Further analysis of the graphite Raman spectrum was conducted in terms of the crystallization of the graphite. The results show that most graphite can be classified into medium to high crystallization grade, with no graphite showing a low crystallization level. Based on the G (1 580 cm^-1), D1(1 350 cm^-1), and D2 (1 620 cm^-1) factors derived from the Raman spectrum of graphite, we apply the carbon material Raman spectroscopy thermometer to calculate the formation temperature of graphite. The results show that the peak metamorphic temperature of Azad-Kashmir sapphire parent rock is over 600 ℃.