Joint 52nd Northeastern Annual Section / 51st North-Central Annual Section Meeting - 2017

Paper No. 7-6
Presentation Time: 8:00 AM-12:00 PM


CARTY, Olin1, ROBERT, Geneviève1 and SMITH, Rebecca2, (1)Department of Geology, Bates College, Carnegie Science Hall, Lewiston, ME 04240, (2)Department of Geosciences, University of Massachusetts Amherst, Morrill Science Center, Amherst, MA 01003; Department of Geology, Bates College, Carnegie Science Hall, Lewiston, ME 04240,

We synthesized glasses along the jadeite-leucite (NaAlSi2O6-KAlSi2O6) join with various amounts of dissolved fluorine (up to 4 wt.%). All fluorine contents quoted are nominal amounts. Na:K ratios synthesized include Jd100, Jd75Lct25, Jd62.5Lct37.5, Jd50Lct50, Jd37.5Lct62.5, and Jd25Lct75, all of which have nominal ratios of non-bridging oxygen to tetrahedrally-coordinated cations (NBO/T) of 0. For Jd50Lct50, we synthesized glasses with 0, 1, 2, 3, and 4 wt.% F. For all other Na:K ratios, we only synthesized glasses with 0 and 2 wt.% F. We measured the viscosity of each melt by parallel-plate viscometry at temperatures between 655°C and 980°C. We use the temperature at which the viscosity is 1012 Pa.s (T12) to compare the effect of F on the different composition melts.

For F contents of 0 and 2 wt.%, at constant temperature, decreasing Na:K ratio increases viscosity. At 825°C, F-free Jd100 has a viscosity ~1.75 log units lower than F-free Jd25Lct75. At the same temperature, but with 2 wt.% dissolved F, Jd100 has a viscosity over ~3 log units lower than Jd25Lct75.

The addition of fluorine decreases the viscosity of each melt relative to its F-free equivalent. With the addition of 2 wt.% F, T12 decreases between 45°C and 130°C for the samples studied. The smallest reduction in T12 is for the Jd25Lct75 composition (45°C) while the largest reduction in T12 is calculated for Jd100 (130°C). The effect of F on viscosity therefore seems to be greater for Na-rich compositions. This is further confirmed in Jd50Lct50 melts for which we synthesized melts with additional nominal F contents. At 825°C, the addition of 1 wt.% F decreases viscosity by nearly 1 log unit. The addition of 2 and 3 wt.% F reduces viscosity by over 1.6 log units and 2 log units, respectively. The addition of 4 wt.% F reduces viscosity by almost 2.7 log units.

We conclude that increasing Na:K ratio and wt.% F both decrease the viscosity of the melts in this study and that dissolved F has a greater effect on the viscosity of Na-rich melts. Our results are consistent with the observed effect of Na:K ratio in more silica rich melts, with albite melt having a viscosity nearly 3 orders of magnitude lower than orthoclase melt at ~925°C. Our results also show a similar effect of F on the viscosity of jadeite and albite melts, with a reduction in T12 for 2 wt.% F of ~130°C in both melts.