The Study On Gemological And Mineralogical Characteristics Of Green-blue Tourmaline In Nuristan, Afghanistan

There have been plenty of researches regarding to the industrial usages oftourmaline in recent years. In the meantime, as a comparatively popular gem in themarket, its gemological characteristics have generally attracted researchers’ attention.This thesis makes a comparison study on zones of tourmaline extracted fromPanshgarskoe mine in Nuristan, Afghanistan, adopting the line mapping method. Thetesting skills include gemology routine testing, polarizing microscopic observation,single-crystal X-ray diffraction analysis, X-ray diffraction analysis, EPMA,, Ramanspectroscopy, infrared spectroscopy and UV-Vis-NIR.According to the gemology routine testing results, the basic gemologicalcharacteristics of tourmaline samples show no obvious inconsistency with that oftourmaline from other parts of the world: its testing data of refractive rate ranges from1.618-1.639to1.624-1.644; its specific gravity ranges from3.031to3.0886, whichrises as its iron content increases; and it is strongly dichroism.The phenomena including inconsistency of the stress inside the crystal amongzones and partial low symmetric indicate that temporary atomic sorting disorderingmight have appeared during crystal growth, stopping it from continuously growing.Another explanation is that there are multiple growing phases.The quantity of SiO2and Al2O3contained in the tourmaline samples from thisarea is basically in accordance with that contained in the crystal bands:38.73%to40.43%of SiO2,38.46%to40.11%of Al2O3and the content ratio of Si and Al isapproximately1. The content ratio of Na and Ca is in positive correlation with thecontent ratio of Fe. There is a significant difference in the quantity of Fe contained indifferent bands and a slight difference in the bands of the same color. The calculatedcrystal chemical formula indicates that a lot of holes exist in X site whereas thenumber of the holes is in positive correlation with the quantity of Al contained in thecrystal.Raman spectra confirmed the chemical composition in different zones and the835cm-1absorption appeared in the iron-rich band is due to Fe-O/SiO4stretchingvibration. Meanwhile, CH3and CH2vibration band at1200cm-1to1600cm-1, C-Ostretching vibration (CO2) at1390cm-1are also detected.1660cm-1vibration onlyexists in the blue-green iron-rich band, indicating condensed ring aromatics C=Cstretching vibration. Carbonaceous materials all exist in the form of fluid saturatedinclusion. Hydroxyl vibration region shows that the increased iron content restrainsthe3650cm-1absorption peak, and contributes to the formation of3570cm-1absorption peak and increases the3680cm-1absorption peak.Raman and infrared spectroscopy confirmed that the sample is elbaite. The bandaroud~5200cm-1can be assigned to H2O. Because these bands still could be observedin infrared spectra while the Y-O-H vibration bands have disappeared after beingheated. In the paper, the hydroxy vibration at3300cm-1to3800cm-1is reassigned andat the same time H2O is believed to occupy the tourmaline X site and lead to3650cm-1.UV-Vis-NIR absorption spectra indicate that, after its formation, the tourmaline samples might have been affected by natural radiation and other factors, which lead tothe variation of its atomic valence.