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The crystal chemistry of paulingite

Dipartimento di Scienze della Terra, Via S. Eufemia 19, I-41100 Modena, Italy

^* E-mail: Elio{at}unimo.it

The crystal chemistry of the uncommon zeolite paulingite, [(K,Na,Ca_0.5,Ba_0.5)₁₀(Al₁₀Si₃₂O₈₄). 30 H₂O; Z = 16] is updated and revised on the basis of chemical compositions and cell constants often samples representative of almost all the occurrences known to date. The framework cation content, defined as R = Si/(Si+Al), shows slight variations ranging from 0.73 to 0.79. The extraframework cations are mainly K, Ca, Na, and minor Ba. Mg and Sr are absent or negligible. The K, Ca and Na contents are extremely variable so that all three types of cation-dominance are found. The cell constant shows small variations (from 35.03 to 35.24 Å) and no significant correlation with the chemical variables. The (K+Na) content is positively correlated with the Si content, and a strong negative correlation between Ca and Na is found. The water content is variable and independent upon the chemical parameters. The dehydration process of the Ca-dominant sample is significantly different from that of both K—and Na-dominant samples.

Key-words: zeolite, paulingite, crystal chemistry, microprobe analysis, paulingite-Na.