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Information × Registration Number 0220U000120, 0115U003008 , R & D reports Title The spectroscopic characteristics and typomorphism of minerals of the ring silicates group popup.stage_title Head Taran M. N., Registration Date 16-01-2020 Organization nstitute of Geochemistry, Mineralogy and Ore Formation popup.description2 By a set of spectroscopic methods, predominantly by Moessbauer, optical absorption and infrared Fourier-spectroscopy, the main minerals of the group of ring silicates, tourmalines, beryls and cordierites, were studied. Among admixed ions of transition metals of the first period, Ti4+, Cr3+, Fe2+ і Fe3+ are prevalent, i.e. those which are most abundant transition metal ions in natural oxygen-based crystals on the whole, which participate in many mineral and rock forming processes, cause color and influence on thermo and electric conductivity and other properties of minerals, rocks, geological complexes and geological landscapes on the whole. Investigation of the optical spectra of tourmalines, beryls and cordierites at different temperatures and pressures revealed that absorption bands of different nature, which are caused by electronic transitions of different types, i.e. dd-transitions within the electronic d-shell of transition metal ions, charge-transfer transitions of metal-metal type and the transitions of exchange-couples of such ions, behave in different ways at influence T and P. On one hand this circumstances is very important for interpretation of the spectra that in many cases is far not unambiguous task, and, on the other hand, gives unique information about electronic state and the related characteristics of minerals at PT-conditions of the earth depths. The studies of Fe- and Fe,Ti-bearing tourmalines have shown that iron ions Fe2+ and Fe3+ occupy predominantly Y-octahedra of the structure. At an increasing oxidation state, i.e. increasing Fe3+-content, intensity of the spin-allowed optical absorption bands of Fe2+ (Y) in E _|_ c polarization quickly increases that evidences of increased concentration of exchange-coupled pairs Fe2+ (Y) - Fe3+ (Y). This process is accompanied by increasing intensity of coloration, the color changing from light-green to dark-blue and, in case of schorls, to black in E c-polarized illumination. In polarization E || c intensity of the above mentioned bands increases at an increasing iron content considerably weaker that in high-iron tourmalines causes appearance of strong dichroism E _|_ c >> E || c. The presence in such tourmalines an admixture of Ті4+ in Y-site of the structure causes an appearance of brownish and brown component in coloration due to a broad absorption Fe2+ + Ті4+ -> Fe3+ + Ті3+ charge-transfer band with maximum, depending on overall chemical composition, from 22000 to 25000 см-1. Investigations of tourmalines of predominant uvite composition with high Mg-content, where the abundance of Mg2+ ion enters the smaller octahedral Z-site, evidences that in difference to other Mg, Fe2+-silicates, no substitution of Mg on Fe2+ in Z-octahedrons takes place and all iron is concentrated in Y-positions. The dark-red color and strong dichroism of high-iron oxi-dravites are caused by high content of Fe3+ ions in Y-site of the structure and appearance of electronic exchange interaction in Fe3+ (Y) - Fe3+ (Y) pairs. Investigation of such crystals at different pressures evidence that the absorption bands in their optical spectra may be interpreted as electronic spin-forbidden transitions of Fe3+ enhanced by such interactions. The detail investigation of chromium-bearing tourmalines from Tanzania is shown that the Usambara-effect (the change of color from green to red at increasing thickness of the sample) by nature is tightly connected to alexandrite effect, but in difference from the latter the color change is caused not the change of spectral composition of illumination, but by a certain balance of optical transmission in two windows of transparency, green and red, and non-linear (exponential) dependence of the optical transmission on the sample thickness. The important condition is a high enough chromium content to form the deep, well resolved windows of transparency in green and red parts of the visible range of the spectra. It is shown how an admixture of other chromophore ions, particularly Fe2+ and Fe3+, may suppress the Usambara-effect in tourmalines. On a large collection of natural and synthetic beryls of different compositions the spectroscopic features of entering of Fe2+ and Fe3+ admixture in the beryl structure and their role in coloration and dichroism of heliodors, aquamarines and various intermediate varieties are established. It is shown for the first time that the space distribution of admixture of Fe2+ in tetrahedral Be-site of the structure along the crystals length is different in the samples from different deposits and may evidence of physico-chemical conditions of their crystallization. The emeralds from Kruta Balka deposit in Peri-Azovian region, Ukraine, their optical and infrared spectra and chemical features are studied in comparison with emeralds from other deposits of the world. The spectroscopic study of bazzite (rear Sc-bearing analogue of beryl) from deposits of Kent (Kazakhstan) and Tordal (Norway) has shown that in difference from ordinary beryls Fe2+- and Fe3+-ions enter exclusively into the octahedral site of the structure. As in beryls the blue coloration and dichroism (E || c > E _|_ c) are caused by charge-transfer band of Fe2+ and Fe3+. The infrared spectroscopy evidences that in difference from beryl, where in structural channels two types of water molecules H2O І and H2O ІІ are usually present, in the bazzites studied only molecules H2O of type II are observed. Product Description popup.authors Ільченко Катерина Олександрівна Гречановська Олена Євгенівна. Лупашко Тетяна Миколаївна Таращан Аркадій Миколайович Хоменко Володимир Михайлович popup.nrat_date 2020-04-02 Close