Atomic Positional Parameters
Na1  4b  0.000  0.500 0.000
Na2 4 atoms not located in cell

O1  16h  0.124  0.418 0.416
O2  16h  0.128  0.197 0.416
O3  16h  0.263  0.373 0.504
O4   8g  0.083  0.305 0.250
O5   8g -0.184 -0.199 0.250

O6   8g -0.186 -0.423 0.250
O7   8e -0.269  0.000 0.000
O8   8d  0.250  0.250 0.000
O9   4c  0.000  0.398 0.250
O10  4c  0.000  0.210 0.250

Si/Al 16h 0.196  0.427 0.536
Si/Al 16h 0.196  0.191 0.540
Si/Al  8g 0.089  0.384 0.250
Si     8g 0.087  0.225 0.250

Reference
Meier WM (1961) Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie, 115, 439.

Mineral Chemistry
An alternative formula for mordenite is (Na₂,Ca,K₂)Al₂Si₁₀O₂₄.7H₂O, which represents the range of possible cation occupancies of channels in the alumino-silicate framework.

This framework is made from complex chains of 5-membered rings composed of SiO₄ and AlO₄ tetrahedra. These rings are cross-linked by 4-tetrahedra rings, to form twisted 12-tetrahedra rings around nearly cylindrical channels parallel to the c-axis. Aluminium is enriched in the 4-tetrahedra rings.

Mordenite forms either from hydrothermal alteration, or from lower temperature transformation, of volcanic glasses. Mordenite-like phases include dachiardite, epistilbite, ferrierite and bikitaite.

Further details about mordenites may be found in the following publications:

Barrer RM (1948) Synthesis and reactions of mordenite. J. Chem. Soc., 2158-2163.

Gottardi G and Galli E, Natural Zeolites (1985) Springer-Verlag, Berlin.

Passaglia E (1975) The crystal chemistry of mordenite. Contr. Min. Pet., 50, 65-77.

The CHIME figure shows sodium ions as large blue spheres, oxygens as small red spheres, and silicons/aluminiums as small ochre spheres. The positions of water molecules in the channels are not shown. The unit cell is outlined.