Structures of minerals with OH attached to Si and their properties.

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1. Refinement of the crystal structure of Al-rich pumpellyite from Sanbagawa, Gunma Prefecture, Japan, was carried out by a least squares method with X-ray single-crystal counter-collected data. The positions of hydrogen atoms have been determined based on the difference Fourier maps, and are consistent with the results deduced from bond-valence calculations. This crystal has the following characters: the double tetrahedral unit [Si_2O_6(OH)] characteristically has a hydroxide group directly attached to Si atom; one of two kinds of octahedral sites is occupied by an aluminum ion in preference to the others; the other octahedral site if occupied by both divalent and trivalent ions , and the electric charge of the latter site is compensted by the amount of hydrogen atoms. We could not find Fe and Mn single pumpellyite crystals.2. Refinement of the crystal structure of P/nnc-vesuvianite from Nakatatsu mine, Fukui Prefecture, Japan,was done using X-ray single - crystal diffraction data. From bond-valence calculations, the proton donor atoms are both O (11) and O (10). The B-sites(square pyramid ) are half occupied by Fe atoms3. Other studies related to this project.3(1) Crystal structure refinements tridymite and Ag_3AsSe_3. structural change of orthorhombic-I tridymite with temperature and high-order thermal motion tensor analyses of high temperature tridymite have been carried out using X-ray single -crystal diffraction data. The crystal structure of Ag_3AsSe_3 has been refined based on high-order thermal motion tensors.3(2) The structural and elastic properties of high-pressure phases of MgSiO_3 are investigated with a computational model based on energy minimization in collaboration with Masanori Matsui, Kanazawa Medical University.3(3) The crystallographic orbits have been studied in collaboration with Wondratschek, Germany. The non-characteristic orbits of the plane have been derived.