Compressional pathways of α-cristobalite, structure of cristobalite X-I, and towards the understanding of seifertite formation

Ana Černok (), Katharina Marquardt, Razvan Caracas (), Elena Bykova, Gerlinde Habler, Hanns-Peter Liermann, Michael Hanfland, Mohamed Mezouar, Ema Bobocioiu and Leonid Dubrovinsky
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Ana Černok: Bayerisches Geoinstitut
Katharina Marquardt: Bayerisches Geoinstitut
Razvan Caracas: CNRS, Laboratoire de Geologie de Lyon, UMR 5276, Université Claude Bernard Lyon 1
Elena Bykova: Bayerisches Geoinstitut
Gerlinde Habler: University of Vienna
Hanns-Peter Liermann: Photon Sciences, Deutsches Elektronen-Synchrotron (DESY)
Michael Hanfland: European Synchrotron Radiation Facility (ESRF)
Mohamed Mezouar: European Synchrotron Radiation Facility (ESRF)
Ema Bobocioiu: CNRS, Laboratoire de Geologie de Lyon, UMR 5276, Université Claude Bernard Lyon 1
Leonid Dubrovinsky: Bayerisches Geoinstitut

Nature Communications, 2017, vol. 8, issue 1, 1-10

Abstract: Abstract In various shocked meteorites, low-pressure silica polymorph α-cristobalite is commonly found in close spatial relation with the densest known SiO2 polymorph seifertite, which is stable above ∼80 GPa. We demonstrate that under hydrostatic pressure α-cristobalite remains untransformed up to at least 15 GPa. In quasi-hydrostatic experiments, above 11 GPa cristobalite X-I forms—a monoclinic polymorph built out of silicon octahedra; the phase is not quenchable and back-transforms to α-cristobalite on decompression. There are no other known silica polymorphs, which transform to an octahedra-based structure at such low pressures upon compression at room temperature. Further compression in non-hydrostatic conditions of cristobalite X-I eventually leads to the formation of quenchable seifertite-like phase. Our results demonstrate that the presence of α-cristobalite in shocked meteorites or rocks does not exclude that materials experienced high pressure, nor is the presence of seifertite necessarily indicative of extremely high peak shock pressures.

Date: 2017
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DOI: 10.1038/ncomms15647

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