Research On Gemological Mineralogy Of Rubies&Aapphires, Color Cause And Enhancement Process Of Rubies From Huadian

Although the demand of ruby and sapphire increases continuously all around the world, the gem-quality sources are becoming less and less. Recently, a placer corundum deposit was discovered in Huadian area, Ji lin Province, with some large-size rubies and sapphires. The previous research focused on the geological characteristics and lack of gemological and mineralogical investigation to provide the support for gemstone enhancement and quality evaluation. So in this paper, the mineral composition, chemical materials and gemological features will be tested by different analysis, and color cause and the factors which may influence the transparency would be proposed for further enhancement experiements.According to the results of polarization microscope, scanning electronic microscope,EPMA and XRF, Huadian rubies contain many kinds of mineral inclusions（e.g.,melilite, mica and ilmenite）, and fractures. These inclusions and fractures are two main factors which may influence the transparency of Huadian rubies.Combined with results of EPMA, LA-ICP-MS, Infrared spectra, UV-Vis spectra and EDS, the color cause of Huadian rubies was attributed to Cr. The average of Cr contents in all samples was 0.31%. The d-d orbit of Cr³⁺ absorbed blue-violet lights near 550 nm and 400nm; and red fluorescence stimulation at 693 nm was the main cause of red color of Huadian rubies. There’re some small amounts of Fe and Ti as Fe2+/Fe³⁺ and Ti4+ with contents of 0.68%（Fe2O3）and 0.02%（Ti O2）, respectively. The electron transfer within Fe2+-Ti4+ may cause the absorption at 560 nm with purple-red disappearance, and O2-àFe³⁺ may cause yellow to brown colors.The color enhancement experiments of rubies might be controlled by testing temperature, the gradient of temperature, time of constant temperature, different fluxes and filling conditions.