Heulandite-Na Gunter M E, Armbruster T, Kohler T, Knowles C R American Mineralogist 79 (1994) 675-682 Crystal structure and optical properties of Na- and Pb-exchanged heulandite-group zeolites Sample: Na-exchanged Atomic parameters from ICSD _database_code_amcsd 0001669 17.767 17.977 7.422 90 116.14 90 C2/m atom x y z occ Biso Na1 .1726 0 .689 .80 10.3 Na2 .5392 0 .243 .84 7.3 Na3 .2839 0 .029 .16 16.1 Si1 .1788 .1698 .0958 .753 1.49 Al1 .1788 .1698 .0958 .247 1.49 Si2 .2864 .0892 .4949 .753 1.53 Al2 .2864 .0892 .4949 .247 1.53 Si3 .2905 .3098 .2826 .753 1.52 Al3 .2905 .3098 .2826 .247 1.52 Si4 .0673 .2978 .4171 .753 1.52 Al4 .0673 .2978 .4171 .247 1.52 Si5 0 .2165 0 .753 1.6 Al5 0 .2165 0 .247 1.6 O1 .3026 0 .537 2.4 O2 .2341 .1197 .6182 3.23 O3 .1879 .1556 .891 4. O4 .2311 .1033 .2498 2.79 O5 0 .3218 .5 3.8 O6 .0807 .1609 .0493 2.83 O7 .3737 .2686 .4492 3.37 O8 .0145 .2709 .1862 3.4 O9 .2123 .2521 .1875 2.93 O10 .1199 .3719 .4212 2.99 OH11 .2839 0 .029 .68 16.1 OH12 .5 0 .5 13.6 OH13 .422 .0814 .035 13.1 OH14 .074 0 .04 .56 26.9 OH15 .082 0 .271 25.4 OH16 .072 -.029 .758 .37 11.84 O17 0 .1 .5 22.2