Pressure-induced transformations of cristobalite

X-ray in situ studies in electrically and laser-heated diamond anvil cells (DACs) at pressures over 80 cpa and temperatures above 2500 K were used to determine stable silica phase at extreme conditions. We demonstrate that so far unidentified phases obtained on the compression of cc-cristobalite, new dense silica polymorph in the Martian Shergotty meteorite, and controversial post-stishovite phase is alpha -PbO2-like silica. (C) 2001 Elsevier Science B.V. All rights reserved.