Shock metamorphism of silicate glasses

Abstract

The changes in refractive index caused by shock compression have been determined for tektite, soda-lime, and silica glasses shocked to pressures up to 460 kb. For shock compression below 80 kb for fused silica and 40 kb for tektite and soda-lime glasses, compression is reversible as the refractive indices are within 0.0025 of the starting values. Index increases of 0.01, 0.04, and 0.06 are observed for soda-lime, tektite, and silica glasses shocked to pressures of 80, 130, and 140 kb respectively. For soda-lime glass subjected to shock pressures between 80 and 230 kb there is a decrease in the postshock refractive index to n=1.5211 at 230 kb. For fused silica shocked to pressures of 140 to 460 kb, refractive index drops from 1.52 to 1.47. The reasons for these decreases in index are not obvious. New values for postshock temperatures for fused silica based on release adiabat data, e.g. ∼1000°C for a shock state at 250 kb, suggest that the decreases in refractive index are caused by a combination of decompression along release adiabats and reconstructive transformation from a shock-induced stishovitelike phase to a low-density glass. Postshock densities calculated from the refractive index data agree closely with those calculated from the release adiabat data.