Heulandite-Ca 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: nonexchanged Atomic parameters from ICSD _database_code_amcsd 0001668 17.671 17.875 7.412 90 116.39 90 C2/m atom x y z occ Biso Na1 .1549 0 .6666 .228 6.3 Ca1 .1549 0 .6666 .44 6.3 Ca2 .5402 0 .2031 .484 2.74 K .2763 0 .01 .03 9.9 Na2 .2763 0 .01 .097 9.9 Si1 .1794 .1698 .0967 .753 1.34 Al1 .1794 .1698 .0967 .247 1.34 Si2 .2886 .0899 .5008 .753 1.42 Al2 .2886 .0899 .5008 .247 1.42 Si3 .2917 .3096 .2831 .753 1.35 Al3 .2917 .3096 .2831 .247 1.35 Si4 .0646 .2984 .411 .753 1.34 Al4 .0646 .2984 .411 .247 1.34 Si5 0 .2131 0 .753 1.4 Al5 0 .2131 0 .247 1.4 O1 .3048 0 .5466 2.8 O2 .2313 .1194 .6132 3.05 O3 .1833 .1543 .8842 3.22 O4 .2385 .1065 .2555 2.45 O5 0 .3259 .5 3.4 O6 .082 .1587 .0626 2.22 O7 .3729 .266 .4508 3.26 O8 .0089 .2662 .1842 2.78 O9 .2103 .2542 .1783 2.64 O10 .1155 .3723 .3988 2.64 OH11 .2763 0 .01 .83 9.9 OH12 .5 0 .5 7.9 OH13 .4228 .0817 .0307 5.4 OH14 .094 0 .285 13.2 OH15 .082 .005 .867 .43 11.84 OH16 0 .0873 .5 20.5