data_global _chemical_name_mineral 'Tridymite' loop_ _publ_author_name 'Kihara K' 'Matsumoto T' 'Imamura M' _journal_name_full 'Zeitschrift fur Kristallographie' _journal_volume 177 _journal_year 1986 _journal_page_first 27 _journal_page_last 38 _publ_section_title ; Structural change of orthorhombic-I tridymite with temperature: A study based on second-order thermal-vibrational parameters Note: hexagonal Gibbs model, T = 733 K ; _database_code_amcsd 0020938 _chemical_compound_source 'synthetic refractory silica brick' _chemical_formula_sum 'Si O2' _cell_length_a 5.052 _cell_length_b 5.052 _cell_length_c 8.27 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 120 _cell_volume 182.794 _exptl_crystal_density_diffrn 2.183 _symmetry_space_group_name_H-M 'P 63/m m c' loop_ _space_group_symop_operation_xyz 'x,y,z' '-x,-x+y,1/2+z' 'x,x-y,1/2-z' '-x+y,-x,1/2-z' 'x-y,x,1/2+z' '-y,-x,z' 'y,x,-z' 'y,-x+y,-z' '-y,x-y,z' 'x-y,-y,1/2+z' '-x+y,y,1/2-z' 'x,y,1/2-z' '-x,-y,1/2+z' 'x,x-y,z' '-x,-x+y,-z' 'x-y,x,-z' '-x+y,-x,z' 'y,x,1/2+z' '-y,-x,1/2-z' '-y,x-y,1/2-z' 'y,-x+y,1/2+z' '-x+y,y,z' 'x-y,-y,-z' '-x,-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Si 0.33333 0.66667 0.43780 O1 0.33333 0.66667 0.25000 O2 0.00000 0.50000 0.00000 loop_ _atom_site_aniso_label _atom_site_aniso_U_11 _atom_site_aniso_U_22 _atom_site_aniso_U_33 _atom_site_aniso_U_12 _atom_site_aniso_U_13 _atom_site_aniso_U_23 Si 0.04577 0.04577 0.04019 0.02289 0.00000 0.00000 O1 0.13344 0.13344 0.04296 0.06672 0.00000 0.00000 O2 0.05586 0.14420 0.13998 0.02803 -0.04619 -0.02310