Determination of the Effects of the Thermal Enhancement Process on Gemstones Using X-ray Diffraction and Raman Spectroscopy

Abstract

This study determined the effects of an optimized thermal enhancement process on the quality of the ruby, sapphire, amethyst, and smoky quartz gem samples from Taita-Taveta County in Kenya. The study sought to improve the quality of low-grade gems by enhancing their color, clarity, and luster and, in turn, improving their competitiveness in the gem market because; the quality of the more significant percentage of gems in Taita-Taveta are low- grade when compared to the high-grade gems in the global market. Thermal enhancement was done using a muffle furnace, a standard cost method that alters the primary molecular structure of the natural gem mineral, thus changing its optical properties. It, in turn, alters the color, luster, cleavage, reflectance, and transparency. When the gem impurities are exposed to heat, they react differently, changing the molecular bonding and hence the overall atomic structure of the gem. After enhancement, the mineralogical, chemical, and morphological changes were analyzed using the X-Ray Diffraction powder method and Raman Spectroscopy. The study established that there was a notable color change for each selected gem sample as temperature increased. The optimum temperature is the one where there is an expected change in color, enhanced clarity, the deepness of color, and reduction in zoning. The study established optimum temperatures for the selected gem samples at 12000C for rubies and sapphires, 450-5500C for amethyst, and 600-6500C for smoky quartz. The changes in ruby and sapphire ranged from deepening of the color, improved luster, and enhanced clarity by removing some impurities and removal of secondary zoning colors. Amethyst and smoky quartz were changed in color to citrine. It also established that the above physical changes were caused by chemical changes in the gems after the thermal enhancement process. The crystal structure of the corundum and quartz samples remained the same even after heating. There were similarities and differences between the thermally enhanced gems of Taita-Taveta and those from other Mozambique belt areas. The thermal enhancement process improved the low-quality gemstones and thus moving them to a different grade. Therefore, it is recommended that thermal enhancement be used to improve the quality of gems in Taita-Taveta at a large scale level. Further research should also be carried out with modern instruments for thermal enhancement and analytical methods for quantification.