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The Si-Al ordering in two contrasting samples of leucite was studied using MAS NMR. One sample was synthesized by performing an ion exchange, in molten KCl, on a natural analcite specimen that had a small distribution of Al next-nearest neighbors (NNN). The other leucite sample was a typical natural specimen from the Alban Hills. In the specimen derived by ion exchange, 45-50% of the Al is on T2 sites with the remainder distributed approximately equally between the T1 and T3 sites. The  29 Si peak positions in this sample resolve a debate in the literature over assignment of the more complex  29 Si spectra of natural leucite specimens. It is possible to simulate the  29 Si spectrum of Alban Hills leucite with a wide variety of Al distributions, including either Al ordering onto T2 or Al ordering onto T1 + T3. By analogy with the analcite-derived sample and considering previous neutron and X-ray data, Al ordering onto T2 is considered somewhat more probable than the alternative schemes.

Si-Al order in leucite revisited: New information from an analcite-derived analogue