Crystal chemistry of stilbites: structure refinements of one normal and four chemically anomalous samples.

Structural refinements were performed on four stilbites with 'anomalous' chemical compositions as regards the monovalent/divalent cation ratio, and a 'normal' stilbite. The four anomalous samples showed, moreover, a monoclinic angle lower than that expected from an empirical correlation between monovalent cation content and ~ angle. In all samples the two cationic sites characteristic of stilbite, were found; in only one sample was a new cationic site localized. One site is fully occupied by Ca alone, or, with some Na, whereas the other sites are fully or partially occupied by monovalent cations only. In the five stilbites, different numbers of water molecule sites were localized. The frameworks, however, seem to be unaffected by the number and composition of extraframework sites. The small [3 angle of the anomalous samples was only partially explained by structural data.