Compressional pathways of alpha-cristobalite, structure of cristobalite X-I, and towards the understanding of seifertite formation - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Nature Communications Année : 2017

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

Résumé

In various shocked meteorites, low-pressure silica polymorph alpha-cristobalite is commonly found in close spatial relation with the densest known SiO2 polymorph seifertite, which is stable above similar to 80 GPa. We demonstrate that under hydrostatic pressure alpha-cristobalite remains untransformed up to at least 15 GPa. In quasi-hydrostatic experiments, above 11GPa cristobalite X-I forms-a monoclinic polymorph built out of silicon octahedra; the phase is not quenchable and back-transforms to alpha-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 alpha-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
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Dates et versions

hal-01692158 , version 1 (24-01-2018)

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Ana Cernok, Katharina Marquardt, Razvan Caracas, Elena Bykova, Gerlinde Habler, et al.. Compressional pathways of alpha-cristobalite, structure of cristobalite X-I, and towards the understanding of seifertite formation. Nature Communications, 2017, 8, 10 p. ⟨10.1038/ncomms15647⟩. ⟨hal-01692158⟩
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