With the increasing interest in gemstones, which have started to offer an important underground wealth for countries. Menderes Massive is one of the most widespread and most important areas of bauxite deposites in the Turkey. Gemstone quality diaspore crystals are formed only within these deposits. In this study, diaspore formations in the southwest wing of the Menderes Massive (Aydın - Muğla) were examined and their geological, geochemical and gemological properties/characteristics were investigated. Bauxite deposits in the study area are observed along the discordance between white crystallized limestone (lower) and gray-dun colored crystallized limestone (upper) contact. The deposits generally extend in NW - SE direction and the samples show massive, pisolotic, oolitic and leopard texture. Diaspore crystals of different lengths and colors are unique to our country, which starting from Bafa Lake and advancing towards Yatağan in the form of dashed arc. It has been extracted as a by-product as a result of diasporitic bauxite production in a single mine for many years and it is not thought to have an economic value. 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.

Diaspore, is related to bauxite in terms of its formation mechanism. Diaspore is one of the gemstone quality stones used in jewelry and jewelry making. It is possible to come across gemstones in various regions of the world. In our country, there are gemstone deposits in all regions. In these deposits, diaspore crystals are considered very valuable. Within the scope of this study, it was aimed to determine the gemological features of the diaspore formations in Sodra (Milas-Mugla) and its surroundings, as well as to determine other minerals and their formation conditions. Main oxide, trace, and rare earth element analyses were performed on seven collected samples. The classification was made using the Al2O3-SiO2-Fe2O3 triangular variation and it was determined that bauxite samples were in the “ferric bauxite” and “bauxite” areas. SEM imaging and EDS analyzes were performed on the samples and according to this result, it was determined that the samples mainly contained O, Al, and Si. The data obtained as a result of Raman Spectroscopy were matched with the device’s own data library and it was determined that the samples taken from the Sodra region were diaspore. In addition, according to the results of the FTIR analysis performed on the faceted sample taken from the Sodra region, it was seen that the samples were compatible with the reference standards and it was scientifically proven to be a diaspore crystal with gemstone quality. During the field studies carried out in the study area, diaspore crystals were encountered in the Milas-Sodra region, together with chloritoid and muscovite, within the metabauxite formations and in the altered zones close to the metabauxite limestone contact. Rock were classified as “muscovitequartzschist,” “quartzschist” with grano-lepidoblastic texture, “micaquartzschist” with lepidoblastic texture, “phyllite” with lepidoblastic texture, and “chlorite-epidote fels” with nematoblastic texture as a result of petrographic analyzes performed on the country rock samples. It is predicted that these gemstone-quality diaspore crystals can be evaluated economically.