Temperatures in the high pressure shock state have been determined by messurement of optical radiation from pure samples of forsterite (Mg2SiO4), &agr;--quartz, and fused silica. Shock waves of known amplitude were produced by tantalum flyer impact using a two-stage light gas gun. Shock pressures in the ranges 150--175 GPa and 70--115 GPa for Mg2SiO4 and SiO2 respectively were achieved, and temperatures in the range 4500--6800 K were measured. The observed temperatures in Mg2SiO4 are consistent with the occurrence of a shock-induced phase transition with a transition energy of ~1.5MJ/kg. Measured Hugoniot temperatures versus pressure in both fused and crystalline SiO2 shcoked to the stishovite regime suggest the occurrence of a previously unknown transition, beginning at pressures of approximately 107 GPa and 70 GPa for &agr;--quartz and fused quartz, respectively. The energies and temperatures appear to be consistent with the onset of melting of stishovite under shock loading.