Recent advances in the high-pressure and high-temperature X-ray diffraction technique are generally reviewed with special reference to geophysical problems relating to phase changes and compression behaviour of the materials in the earth's interior. It is emphasized that the high-power X-ray source is extremely useful for the X-ray diffraction under very high pressure. Energy-dispersive type X-ray diffraction technique using the high-power polychromatic X-rays from SOR will improve the high-tempera-ture limit of the high-pressure X-ray study. SOR is hopefully applied to the X-ray diffraction study under deep mantle conditions, simultaneously to 200-1000 kbar and 1000-3000°C. An account is also given that SOR will be a powerful tool to investigate by diffraction, microcrystals or microtextures of minerals.
