CCA-2688 Conference Paper Recent Contributions and Modern Perspectives in XRD Studies of Minerals*

Some exciting recent developments in the field of mineralogical crystallography are considered. The crystal chemical phenomena (e.g. ionic ordering, polyhedral stacking variations, microtwinning, modulation), which accompany the formation of real structures, are discussed on the basis of structural studies of a large group of minerals, recently investigated in the Moscow State University. The new approaches used for their investigation allowed extending the scientific ideas connected with: the composition and structure of the deep geospheres, structural classification of minerals, forms of concentration of chemical elements in the Earth's crust, further development of modular theory and other problems of modern struc-tural mineralogy. The advantage of using synchrotron radiation opens the gate to a new branch of microgeochemistry (about 20 % of known minerals lack structure determination, mainly because crys-tals are too small or imperfect for laboratory X-ray sources). Stu-dies of the phase transitions of mantle minerals at high pressure and high temperature contribute to a better understanding of the composition, structure and geodynamics of the deep geospheres. A new model of the mantle, based on the most recent seismotomogra-phic data and on the phase transition studies of mantle minerals, is reported. Several concentric bands are revealed in the mantle, although the previous model emphasized its subdivision only in two parts: upper and lower. New approaches to the XRD studies of * Based upon the plenary lecture presented at the 8th Croatian-Slovenian Crystallographi