Structural study of mordenite from Mátra Mts. (N-Hungary): dachiardite moduls reduce channel size in mordenite

Zeolites are crystalline microporous alumosilicates whose unique pore and channel systems are the reason for their important role in catalysis, separation, and ion exchange. This work focuses on the morphology and structure of a natural zeolite, mordenite. Our samples were collected at Lengyendi-galya (Gyökeres-tető) in the Mátra Mountains (NE-Hungary). Zeolite samples were investigated by X-ray powder diffraction, scanning, and transmission electron microscopy. Mordenite has typically fibrous appearance and occurs in association with other zeolites such as heulandite and chabazite. Based on intense streaks and superlattice reflections in selected area electron diffraction patterns, we identified planar faults in the structure. A single fault produces a dachiardite-type structural slab within the mordenite lattice, reducing its channel size.