Dingwell, Donald B.; Webb, Sharon L.
The fluxing effect of fluorine at magmatic temperatures (600-800 °C): A scanning calorimetric study.
In: American Mineralogist, Vol. 77, No. 1-2: pp. 30-33
The effect of F on the glass transition behavior of albite, diopside, and four other silicate
melts has been investigated using scanning calorimetry. The addition of F to all silicate
melts investigated results in a strong, nonlinear decrease of the glass transition temperature
(Z' as recorded by the peak temperatures of heat capacity). The decreases observed extrapolate
consistently to published fluoride glass transition temperatures. The largest Z,
decrease is observed for albite-FrO-, melts (AT = 250 °C at 6 wt%F ). The effect of F is
similar to that previously observed for HrO (Taniguchi, 1981).
Physical properties of low-temperature silicate liquids are a valuable constraint on lowtemperature
petrogenetic processes in granite and pegmatite petrogenesis. Low-temperature
wiscosities can be estimated from the glass transition data. These data are combined
with previously published high-temperature, concentric-cylinder viscosity data to obtain
a much more complete description of the temperature dependence of viscosity for these
The present data, obtained on supercooled liquids close to the glass transition, are of
special significance because it is at the glass transition that silicate glass structures are
frozen. A separate multinuclear NMR study of glasses quenched from these experiments
has shown that the predominant coordination of F in albite glass is octahedral to Al. The
coordination state of F does not appear to be concentration dependent, and thus the
structural origin of the nonlinear Z, decrease does not arise from such a mechanism.