Abstract
Interest in gemstones, which have been used as symbols of beauty, wealth and status since prehistoric times, has increased in recent years and taken an important place in many countries. The Menderes Massif is the most important area where bauxite deposits are observed in Turkey. Gemstone quality diaspore crystals are formed only in these deposits. In this study, the mineralogical, geochemical and gemological features of the diaspore formations on the south-western side of the Menderes Massif (Bafa Lake - Milas) were investigated. In field studies carried out in the study area, diaspore crystals were found in the Pınarcık region, located between Bafa Lake and Milas, within metabauxite formations together with chloritoid and muscovite, and in some places were encountered in altered zones close to the metabauxite limestone contact. As a result of petrographic analyses of the wallrock samples, grano-lepidoblastic textured “muscovite-quartzschist”, “quartz-phyllite”, “mica-quartzschist” and lepidoblastic textured “phyllite”, and nematoblastic textured “greenschist-chlorite-epidote fels” rocks were identified. To evaluate the main oxide, traces and rare earth elements on the 28 collected samples, Al2O3-SiO2-Fe2O3 triangular variation was used. According to the classification, the bauxite samples were determined to be in the "ferric bauxite" and "bauxite" areas. As a result of SEM imaging and EDS analyses performed on the samples, it was determined that the samples mainly contained O, Al and Si. K, Na, Fe, Ca and Mg were also found close to these elements. Using Raman Spectroscopy, in the light of matching values obtained from the microscope's own database, it was seen that the samples taken from Pınarcık (PI) region were diaspore, and brucite (Mg(OH)2)) and ugillite (Ca3(Ti, Al, Zr)9O20) minerals were also detected. In addition, FTIR analysis was performed on 4 samples taken from Pınarcık (PI) region and according to the results of their analysis, it was seen that the samples were compatible with standard wavelength references. It was scientifically proven that the samples collected from the region and subjected to facet processing are gemstone quality diaspore crystals with various color variations. This study will make an important contribution to understanding the properties of the gemstone quality diaspore mineral, its formation, and finding similar formations in the region.Diaspore formations in the study area are generally observed as lenticular, brecciated, cracked and pockets in crystallized limestones, bauxite and altered zones with calcite, muscovite and chloritoid minerals. Diaspores are generally observed in the form of sheet around Milas. Increased interest in diaspore crystal, especially in the last 30 years and this study will be important in terms of gaining the deserved value of diaspore crystal which is unique to our country. Since it is likely that new diaspore deposits will be found in the region, further studies are planned on this subject. The data to be obtained will be important in the determination of new diaspore deposits.