Viscosity and water content of rhyolite glass

We determined the viscosity of rhyolite glass at temperatures between 350° and 850°C, water pressures between zero and 68.9 bars, and water content between 0.1 and 3 weight per cent. Our technique was to construct a compaction rate curve for the rhyolite glass under known conditions of temperature, water pressure, and compaction load. A similar set of compaction curves was constructed for Corning Pyrex 7740 glass under known temperature and compaction load (but zero water pressure). Since we knew the viscosity of the Pyrex as a function of temperature, we could assign a viscosity to each of the Pyrex compaction rate curves. A comparison of the compaction rate curves of the Pyrex with those of the rhyolite glass allowed us to determine the viscosity associated with each of our rhyolite glass compaction curves. The viscosities range from log η = 9.5 to 14.5. We determined the water content of rhyolite glass at temperatures between 350° and 850°C and water pressures between zero and 68.9 bars. The content of water ranged from less than 0.1 to 3.0 weight percent.