Abstract
While a great deal is known about the interaction between water and rhyolitic glasses and
melts at temperatures above the glass transition, the nature of this interaction at lower
temperatures is much more obscure. Comparisons between high- and low-temperature diffusion
studies suggest that several factors play important roles under lower-temperature conditions that
are not significant at higher temperatures. Water concentrations in rhyolitic glasses hydrated at
low temperatures are significantly greater than in those hydrated at high temperatures and low
pressures. Surface concentrations, which equilibrate quickly with the surrounding environment at
high temperature, change far more slowly as temperature decreases, and may not equilibrate at
room temperature for hundreds or thousands of years. Temperature extrapolations of high-and
low-temperature diffusion data are not consistent, suggesting that a change in mechanism occurs.
These differences may be due to the inability of “self-stress”, caused by the in-diffusing species,
to relax at lower temperature. Preliminary calculations suggest that the level of stress caused by
glass-water interaction may be greater than the tensile strength of the glass. On a microstuctural
scale, extrapolations of high-temperature Fourier transform infrared spectroscopy (FTIR) data to
lower temperatures suggests that there should be little or no hydroxyl present in glasses hydrated
at low temperature. Comparisons of low-temperature hydration results between SiO2, obsidian,
and albite compositions show distinct differences, and features are present in the spectra that do
not occur at high temperature. Analysis of H2O and D2O diffusion also suggest that mechanistic
differences occur between low- and high-temperature diffusive processes
