Na8Si[Si6O18] Fleet M E American Mineralogist 83 (1998) 618-624 Sodium heptasilicate: A high-pressure silicate with six-membered rings of tetrahedra interconnected by SiO6 octahedra: (Na8Si[Si6O18]) _database_code_amcsd 0002009 7.180 7.180 7.180 87.26 87.26 87.26 R-3 atom x y z B(1,1) B(2,2) B(3,3) B(1,2) B(1,3) B(2,3) Na1 .2363 .2363 .2363 .006186 .006186 .006186 0 0 0 Na2 0 .5 .5 .008767 .006770 .007696 -.000974 -.001218 .000828 Na3 .5 0 0 .005406 .005650 .010764 .000292 -.000731 -.000487 Si1 0 0 0 .004384 .004384 .004384 0 0 0 Si2 .2719 .7396 .2715 .004627 .005066 .004968 -.000244 -.000097 -.000195 O1 .2129 .5451 .2128 .008865 .006624 .008134 -.000779 -.002630 -.000536 O2 .1690 .9181 .1692 .006624 .006478 .005212 .000049 -.001072 .000244 O3 .2346 .7653 .4995 .008378 .007939 .005260 .000974 .000292 -.000195