A sample of levyne-Na from Dunseverick, Antrim, Northern Ireland, UK, has been characterized from the crystal chemical and structural point of view. Its mean crystal chemical formula, calculated on the basis of 54(Si+Al), is Na7.72Ca4.62K1.31Sr0.08Mg0.02(Al19.55Si34.45O107.50)·50.5H2O. Levyne-Na is associated with erionite-Na whose chemical formula is Na6.08Ca0.85K2.55Mg0.16(Al10.41Si25.59O72.13)·30.6H2O, calculated on the basis of 36(Si+Al). Their compositions are consistent with those of levyne/erionite inter/overgrowth reported in the literature. The structural analysis, carried out by the Rietveld method on laboratory parallel-beam X-ray powder diffraction data, is in good agreement with the chemical composition representing a significant improvement with respect to the available data so far. Extra-Framework (EF) cations are allocated at four sites, Ca1, Na3, K4 and Na5 with partial occupancy. Water molecules are distributed among five sites. Possible coexistence schemes of cations, forced by the avoidance of short contacts are proposed and validated by bond valence analysis.

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