The Effects of Fluorine on the Viscosity of Melts in the (Na, K) ALSiO4-SiO2 System

New viscosity data is presented for discrete melt compositions across the nephiline-kalsilite ((Na,K)AlSiO4) and jadeite-leucite ((Na,K)AlSi2O6) joins of the (Na, K)AlSiO4-SiO2 melt system assessing the effects of the volatile fluorine on the viscosity of these melts. The sodium-potassium mixing effects described by LeLosq and Neuville (2013) are present in the flourine-free melts, as is evident by the fragility and density plots against mol% K2O/(Na2O+K2O). However, the changes in fragility and density due to the addition of fluorine do not seem to be dependant upon the Na:K ratio as much as the Si:Al ratio. It is proposed tat the pronounced changes in fragility due to the addition of fluorine in both melt systems as a result of 1) a lack of silica, and 2) the affinity of fluorine to cluster with alumina and as opposed to sodium or potassium