The Decomposition of Glass by Water at High Temperatures and Pressures

JSGT 1927 V11 T097-T106 

An important aspect of experimental geochemistry is the determination of the role played by the water in the formation of silicate minerals both in the crystallisation of igneous rocks and in metamorphic processes. The powerful action of water at high temperatures and under correspondingly high pressures has been studied by many observers, and a number of minerals have been found easy to synthesise in bombs capable of withstanding the pressure developed by the water. The experiments have, in the main, been of purely qualitative character; there has been no attempt to control the experimental conditions, and, in particular, to introduce the non-volatile components in a thoroughly homogeneous condition. Silica has been added as quartz or as amorphous silica; alumina as hydrated alumina or as an aluminate; the alkalis as hydroxide or carbonate; and all are introduced as a heterogeneous mixture, often not even mechanically well mixed. Experience has shown that such a mixture is not adequate, and that to ensure equilibrium a material initially more homogeneous should be used. A glass is an excellent form in which to introduce the non-volatile components, because its homogeneity can be determined by microscopic examination, and it is more reactive than initially crystalline material. In our hydrothermal studies we have adopted the procedure of first preparing homogeneous glasses, which are heated in bombs with water, and the product examined with the petrographic microscope to determine the crystalline phases; such a study of alkali–lime–silica and alkali–alumina–silica glasses is under way.

G. W. Morey & N. L. Bowen