Line and Kearley, 1998, started their discussion about the librational and vibrational spectra of water in natrolite, from the structure of the zeolites. These minerals have "three components: the aluminosilicate framework, …, the extraframework cations or anions which balance the charge of the framework, and the water". The "framework charge is delocalised over the whole framework so that in the first approximation it can either be ignored or regarded as a uniform charge density". "The extraframework cations, on the other hand, are almost fully charged and thus constitute the main bonding centres for any polar species, including water". However, the oxygen sites of the framework make hydrogen bonding to the "hydrogen atoms of the polar species, and it is the strength of this bonding which is often of interest. The water can therefore bind to the cations and/or hydrogen bond to the framework". In the case that we have water-water interactions, "the hydrogen bonding to other water molecules is much stronger than that to the framework and therefore dominates". But in natrolite zeolite, "the water molecules are not directly attached to other water molecules. Thus, the nearest-neighbor interaction from the cation can be studied in isolation". The water molecule is "attached to only two cations and has no water molecules in the first hydration shell" (see please the further discussion of interactions in .