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 #9a based on stacking sequence ABABCBAC Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience. ; _database_code_amcsd 0003006 _chemical_formula_sum 'Si Mg O3' _cell_length_a 13.063948 _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 2/c 1' loop_ _space_group_symop_operation_xyz 'x,y,z' 'x,-y,1/2+z' '-x,y,1/2-z' '-x,-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z SiA 0.90625 0.91667 0.08333 SiB 0.84375 0.41667 0.91667 SiC 0.40625 0.91667 0.75000 SiD 0.34375 0.58333 0.41667 Mg1a 0.00000 0.41667 0.25000 Mg2a 0.00000 0.25000 0.75000 Mg1b 0.25000 0.91667 0.08333 Mg2b 0.25000 0.25000 0.08333 Mg1c 0.50000 0.58333 0.75000 Mg2c 0.50000 0.25000 0.75000 O1A 0.81250 0.91667 0.08333 O2A 0.93750 0.75000 0.91667 O3A 0.93750 0.08333 0.91667 O1B 0.93750 0.41667 0.91667 O2B 0.81250 0.25000 0.08333 O3B 0.81250 0.58333 0.08333 O1C 0.31250 0.91667 0.75000 O2C 0.43750 0.75000 0.91667 O3C 0.43750 0.08333 0.91667 O1D 0.43750 0.58333 0.41667 O2D 0.31250 0.75000 0.25000 O3D 0.31250 0.58333 0.75000