Gemmological and mineralogical investigations and genesis of the kammererite from the Kesis (Erzincan) and Kop (Erzurum) mountains

Even though there are many chromitite deposits in Turkey, the most productive chromitite deposits including chromian clinochlore and chromian are present in the eastern Anatolia region. Kammererite (chromian clinochlore), in essence, is one of the rarest clinochlore minerals as a sub-variety of large family of the chlorite minerals. Even though it is the monoclinic IIb-2 polytype, with symmetry C2/m, which is one of the most abundant regular-stacking one-layer chlorites occurring in nature, the crystallization of chromian clinochlore is less abundance. Hence, gem-quality magenta colored kammererite which may be formulized as [Mg5(Al, Cr, Fe)2Si3O10(OH)8] with reference to the abundance of the main oxides in the XRF bulk analyses, is only found in Turkey worldwide. Therefore, they are called Turkish kammererite. Beside of the mineral kammererite, the minerals uvarovite, magnesite, chromian spinel, chlorite and some garnets are also present in the paragenesis. Geological field observations and data in the region reveal that the kammererite specimens are crystallized as remobilized-origin on a chromitite matrix, deposited in the podiform-type chromitite ore deposits, and surrounded by the peridotitic and harzburgitic ultrabasic rocks. Thus, it can be stated that this rare mineral formation is derived from the secondary components of the hydrothermal alteration of the principle amphibole, pyroxene and biotite minerals in the surrounding peridotitic and harzburgitic (partially serpentinitic) rocks where they are embedded throughout the Northeastern Ophiolitic Belt comprising the Kesis and Kop Mountains in the Eastern Anatolia region of Turkey. In this study, unique loose Turkish kammererite crystals were the first time investigated as both mineralogically and gemmologically. Accordingly, the well-known some further spectroscopic analytical methods were used to characterize and identify in detail for provenance and genesis. Firstly, as a structural characterization, in the light of the data obtained from X-ray fluorescence (XRF) and X-ray diffraction (XRD) as well as some essential gemmological measurements and polarizing microscope observations, dispersive confocal (green laser) micro-Raman spectroscopy (DCµRS) shows that the strong micro-Raman bands in the kammererite samples with C and C|| axes are peaked at 681, 541, 353, 197, and 112 cm-1. These bands are a result vibrational and librational symmetric and asymmetric stretching and bending modes of (MgOH)-, (AlOH)2-, (CrOH)2-, (FeOH)2-, and (SiOH)1- molecules, which forms all kammererite structure. Secondly, as a provenance characterization, photoluminescence and cathodoluminescence spectra show that individual luminescence bands in the kammererite samples are due to mainly chemical defects caused by transition metal and rare earth elements in the lattice, which they are detected by the inductive coupled plasma-atomic emission spectroscopy (ICP-AES). Finally, these parameters provide positive identification regarding to geographic origin of the original Turkish kammererite. It can be seen that the obtained micro-Raman bands, specific gravity values, luminescence spectra, and trace element contents give a unique fingerprint for this kind of clinochlore gemstone.