data_global _chemical_name_mineral 'Pyroxene-ideal' loop_ _publ_author_name 'Thompson R M' 'Downs R T' _journal_name_full 'American Mineralogist' _journal_volume 88 _journal_year 2003 _journal_page_first 653 _journal_page_last 666 _publ_section_title ; Model pyroxenes I: Ideal pyroxene topologies Pyroxene #9b based on stacking sequence ABABCBAC Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience. ; _database_code_amcsd 0003007 _chemical_formula_sum 'Si Mg O3' _cell_length_a 13.063945 _cell_length_b 6 _cell_length_c 3.4641016 _cell_angle_alpha 90 _cell_angle_beta 90. _cell_angle_gamma 90 _cell_volume 271.529 _exptl_crystal_density_diffrn 9.823 _symmetry_space_group_name_H-M 'P 1 21/c 1' loop_ _space_group_symop_operation_xyz 'x,y,z' 'x,1/2-y,1/2+z' '-x,1/2+y,1/2-z' '-x,-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z SiA 0.96875 0.16667 0.33333 Mg1a 0.87500 0.66667 0.50000 Mg2a 0.87500 0.00000 0.50000 SiB 0.28125 0.33333 0.16667 SiC 0.21875 0.66667 0.50000 SiD 0.46875 0.16667 0.33333 Mg1b 0.37500 0.66667 0.83333 Mg2b 0.37500 0.00000 0.83333 O1A 0.06250 0.16667 0.33333 O2A 0.93750 0.00000 0.16667 O3A 0.93750 0.33333 0.16667 O1B 0.18750 0.33333 0.16667 O2B 0.31250 0.50000 0.00000 O3B 0.31250 0.33333 0.50000 O1C 0.31250 0.66667 0.50000 O2C 0.18750 0.50000 0.66667 O3C 0.18750 0.66667 0.16667 O1D 0.56250 0.16667 0.33333 O2D 0.43750 0.00000 0.16667 O3D 0.43750 0.33333 0.16667