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The article reports on the recovery of diaspore crystals near Pinarcik, Turkey. It mentions that the best crystals and groups of crystals share all the characteristics that have made the cut stones interesting. It indicates that mining and recovery have emphasized production of gem rough, not mineral specimens. It encourages production of mineral specimens from the deposit.

Abstract: Remobilized-origin gem diaspore and related minerals occur as infill within structurally controlled voids that developed in the upper of two distinct karst unconformity-type metabauxite (diasporite) horizons in the İlbir Mountains area of the Milas-Muğla province, SW Turkey. Colour-change diaspore (trademarked as zultanite) and associated mineral specimens (greenish muscovite, chloritoid, donbassite, specular hematite, ilmenite, goethite, and younger calcite) occur in fracture zones (veins and open structures) that cross-cut the metabauxite horizons. The mineralized fracture zones do not extend into the enclosing marbles, probably because of the ductility contrast between the brittle bauxite and relatively plastic carbonate beds. Thick, white to light gray and dark gray limestone beds were deposited in the İlbir Mountains area during the Cretaceous (146–65Ma), and contain two stratigraphically distinct karst-fill bauxite horizons. Al-, Fe-, Si- and Ti-rich solutions that infiltrated the karstified limestone probably originated from altered schist and gneiss that surround the basin. The limestone beds (>2000m thick) were subjected to burial metamorphism, forming marble. Subsequently, the marble block was folded during nappe emplacement toward the SSW as part of late Alpine contractional deformation during the Paleogene (65–23.8Ma). The upper bauxite horizons within the folded block were cross-cut by fracture zones because of their relatively brittle rheology. At this time, increased pressure and temperature in the bauxite horizons resulted in remobilization of the primary constituents of the bauxite within an aqueous complex, resulting in the crystallization of coarse-grained assemblages in the cross-cutting structures. Ultimately, erosion and mineral exploration revealed the steeply dipping bauxite outcrops and mine workings evident today. This paper focuses on the mine geology of surface outcrops of diasporic bauxite, the upper bauxite horizon within underground mine galleries at elevations of 600, 632, 637, 642, 652, 657, and 702m, and in open pits at sites in the Küçükçamlık and Büyükçamlık hills, Milas-Muğla province, SW Turkey. [Copyright &y& Elsevier]

Abstract: The İlbirdağı diasporic metabauxite (diasporite) deposit of the Milas (Muğla) region of Turkey is a unique deposit including both metamorphic (primary) and hydrothermal-remobilized (secondary) diaspore that formed during different geological periods. Microscopic diaspore crystals with a metamorphic origin are common and are the main constituent of the metabauxite ore, which was metamorphosed during from the Late Cretaceous to Late Paleocene Periods. However, secondary macroscopic diaspore crystals filling fracture zones that crosscut the metabauxite ore formed during the Late Paleocene, Eocene and Oligocene Periods as the result of later hydrothermal solutions that remobilized constituents of the metabauxite. The macroscopic diaspore crystals can be distinguished from the metamorphosed microscopic diaspore crystals, based on size, appearance, occurrence, and origin. Approximately 60% of the macroscopic diaspore crystals have an opaque appearance and pale green coloration and are not considered attractive. By contrast, the other 40% are gem quality and exhibit a marked change in color under different types of illumination. The crystals are mostly olive-green and soil-brown in daylight. A small number of the crystals display color-change, such as green in daylight or equivalent illumination and carmine in low-wattage tungsten lights. X-ray diffraction (XRD) study, using a comparative matching technique, reveals that these Anatolian diaspore (zultanite) crystals [AlO(OH)] are polycrystalline and that their X-ray spectrum includes the overlapped XRD peaks of some mineral inclusions consisting of donbassite [Al5.33Si3O10(OH)8] (di-di-octahedral sheeted Al-rich chlorite), corundum (Al2O3), boehmite [AlO(OH)], quartz (SiO2), ilmenite (FeTiO3), goethite [FeO(OH)] and chloritoid [(Fe, Mg, Mn)2Al4Si2O10(OH)4]. We label these unusual inclusions as sub-microscopic inclusions, because they cannot be seen with a polarizing microscope. Polarizing microscope (PM), scanning electron microscope (SEM), optical absorption (OA), Fourier transform-infrared (FT-IR) and simultaneous differential-thermogravimetric analysis (DTA/TGA) investigations were performed to reveal the mineralogical characteristics of the Anatolian diaspore crystals. [Copyright &y& Elsevier]

Abstract: Fire opal (SiO2·nH2O) and diaspore [Al(OH)O] are two different precious and rare mineral species with high water content. While these species are being cut and polished to make gems, defect-induced weaknesses such as fragility, splintering, and cracking become apparent since the temperature of the mineral species may be increased to high temperatures during the process. These deformations may be broadly related to water loss (molecular (H2O) and hydroxyl (OH) group) and transformation of the base building components and/or inclusion minerals. In this study, thermal properties and thermal stability as dehydratial behaviors of both gem quality fire opal (SiO2·nH2O) from the Şaphane region (Kütahya, Turkey) and gem quality diaspore (AlOHO) from the Milas region (Mug˘la, Turkey), including some associated mineral inclusions, were studied by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform-Infrared absorption (FTIR) spectroscopy and thermal analysis (DTA/TGA). During heating to 1400°C, DTA/TGA patterns indicated that the weight losses of the fire opal and diaspore were due to the water loss only, and that these losses occur in the temperature ranges between about 342 and 722°C in fire opal, and between about 592 and 718°C in diaspore. In addition, after making some corrections concerning the mass gain observed, being due to the drift with buoyancy effect of the atmosphere, in their TGA curves, the fire opal shows a mass loss of 7.942%, and one distinctive sharp endotherm at 1089.99°C and seven weaker endotherms, whereas the diaspore shows a mass loss of about 13.826%, and one distinctive sharpest endotherm at 650.47°C and four weaker endotherms. [Copyright &y& Elsevier]

Abstract  Several m-thick, karst-unconformity-type metabauxite horizons in the İlbir Mountains of SW Turkey host open-space mineralization of gem-quality diaspore (trademarked as zultanite), associated with muscovite, hematite, ilmenite, chloritoid, and younger calcite. The hydrothermal-metamorphogenic mineralization occurs in fracture zones (veins and open structures) that crosscut the metabauxite horizons, but does not extend into the marble host rocks. The white to dark gray marble sequence (over 2,000 m in thickness) is of Cretaceous depositional age and was affected by Alpine (Paleogene) tectonometamorphism which caused the hydrothermal remobilization of primary bauxite components into crosscutting structures. [ABSTRACT FROM AUTHOR]