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Dear Saibal, It depends whether you are interested in K-Na or (K,Na)Al-Si exchange. These references should help you: Hovis, Guy L.; Crelling, James A. The effects of excess silicon on immiscibility in the nepheline-kalsilite system. American Journal of Science (2000), 300(3), 238-249. Hovis, Guy L.; Roux, Jacques. Thermodynamics of excess silicon in nepheline and kalsilite crystalline solutions. European Journal of Mineralogy (1999), 11(5), 815-827. Hovis, Guy L.; Roux, Jacques. Thermodynamic mixing properties of nepheline-kalsilite crystalline solutions. American Journal of Science (1993), 293(10), 1108-27. Sack, Richard O.; Ghiorso, Mark S. Thermodynamics of feldspathoid solutions. Contributions to Mineralogy and Petrology (1998), 130(3-4), 256-274. Ferry, John M.; Blencoe, James G. Subsolidus phase relations in the nepheline-kalsilite system at 0.5, 2.0, and 5.0 kbar. American Mineralogist (1978), 63(11-12), 1225-40. I believe that Sack-Ghiorso's formulation is also incorporated in the Melts software, David [log in to unmask] wrote: > Hi, > > Could someone please help with information on activity models for > nepheline? Can't seem to find any reference that talks about this. And > yet, I think nepheline is on the THERMOCALC program, but not on AX. > > Saibal Gupta. > > > ***************************************** > This Mail is Certified to be Virus Free. > CIC Network Security Group, IIT Kharagpur > ***************************************** -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ David Dolejs (postdoc/geochemistry) Bayerisches Geoinstitut Universitaet Bayreuth D-95440 Bayreuth Tel: +49 921 553717 Germany Fax: +49 921 553769 http://www.users.bgi.uni-bayreuth.de/~d_dolejs/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~