Water and the density of silicate glasses

A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial molar volume of water i s 12.0 +/- 0.5 cm(3)/mol. This value holds for simple or mineral compositio ns as well as for complex natural glasses, from rhyolite to tephrite compos itions; prepared up to 10-20 kbar pressures and containing up to 7 wt% H2O. This volume does not vary either with the molar volume of the water-free s ilicate phase, with its degree of polymerization or with water speciation. Over a wide range of compositions, this constant value implies that the vol ume change for the reaction between hydroxyl ions and molecular water is ze ro and that. at least in glasses, speciation does not depend on pressure. C onsistent with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO2-M2O systems (M = H, Li, Na, K) suggests that the partia l molar thermal expansion coefficient of H2O is about 4 X 10(-5) K-1 in sil icate glasses.