X-ray diffraction study of phase stability in SiO2 at deep mantle conditions

Sean R. Shieh, Thomas S. Duffy, Guoyin Shen

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32 Scopus citations


The stability of SiO2 phases were examined by X-ray diffraction at pressure up to 131 GPa and temperature > 1300 K, corresponding to Earth's deep lower mantle conditions. Three materials, stishovite, cristobalite, and silica glass were used as starting materials, and an argon pressure-transmitting medium was loaded with the sample for five out of six sets of laser-heated diamond cell experiments. X-ray fluorescent crystals were loaded with the sample to ensure alignment of X-ray beam and heating laser. Our results from three different staring materials indicate that the CaCl2-type phase is the stable phase throughout our studied P-T range. We observe the α-PbO2-type phase for cristobalite starting material at pressures greater than 48 GPa at room temperature. However, this transforms to the CaCl2-type structure upon heating between 72-113 GPa. Transition kinetics and metastability may be important in explaining differences in results reported above 75 GPa, and key experimental variables are discussed.

Original languageEnglish (US)
Pages (from-to)273-282
Number of pages10
JournalEarth and Planetary Science Letters
Issue number1-2
StatePublished - Jun 30 2005

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


  • CaCl-type structure
  • High-pressure
  • Laser-heating
  • Mantle
  • Silica


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