Measurement of density and structure of silicate glasses under high pressure

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We have developed synchrotron X-ray absorption and diffraction techniques for measuring the density and structure of low-Z noncrystalline materials and have applied them to study the behavior of SiO_2 glass up to 100 GPa. The experimental results do not support the hypothesis of dense magma in the deep lower mantle. We also found the interesting behavior of the glass, such as the incorporation of a large amount of helium atoms into interstitial voids and the giant residual anisotropy in the structure upon recovering from high-pressure conditions due to the deformation by nonhydrostatic stresses.