Fedele L.;  Webster J.;  De Vivo B.;  Bodnár R. J.:   The silica under-saturated part of the system NaAlSiO4-SiO2 AT 1 ATM. preliminary data on the effects of fluorine.  In: Acta mineralogica-petrographica, (2).  pp. 65-66. (2003)