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 #6 based on stacking sequence ABABACBC Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience. ; _database_code_amcsd 0003002 _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 c 1' loop_ _space_group_symop_operation_xyz 'x,y,z' 'x,-y,1/2+z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z SiA 0.96875 0.91667 0.16667 SiB 0.90625 0.41667 0.00000 Mg1a 0.81250 0.08333 0.00000 Mg2a 0.81250 0.75000 0.00000 SiC 0.71875 0.41667 0.66667 SiD 0.65625 0.08333 0.33333 Mg1b 0.56250 0.41667 0.33333 Mg2b 0.56250 0.75000 0.33333 SiE 0.40625 0.58333 0.50000 SiF 0.46875 0.08333 0.33333 Mg1c 0.31250 0.08333 0.66667 Mg2c 0.31250 0.75000 0.66667 SiG 0.15625 0.08333 0.00000 SiH 0.21875 0.41667 0.33333 Mg1d 0.06250 0.41667 0.66667 Mg2d 0.06250 0.25000 0.16667 O1A 0.87500 0.91667 0.16667 O2A 0.00000 0.75000 0.00000 O3A 0.00000 0.08333 0.00000 O1B 0.00000 0.41667 0.00000 O2B 0.87500 0.58333 0.16667 O3B 0.87500 0.75000 0.66667 O1C 0.62500 0.41667 0.66667 O2C 0.75000 0.25000 0.83333 O3C 0.75000 0.41667 0.33333 O1D 0.75000 0.08333 0.33333 O2D 0.62500 0.25000 0.16667 O3D 0.62500 0.91667 0.16667 O1E 0.50000 0.41667 0.00000 O2E 0.37500 0.75000 0.33333 O3E 0.37500 0.41667 0.33333 O1F 0.37500 0.08333 0.33333 O2F 0.50000 0.75000 0.00000 O3F 0.50000 0.08333 0.00000 O1G 0.25000 0.08333 0.00000 O2G 0.12500 0.75000 0.33333 O3G 0.12500 0.08333 0.33333 O1H 0.12500 0.41667 0.33333 O2H 0.25000 0.25000 0.50000 O3H 0.25000 0.41667 0.00000