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
Domaines
Sciences de la Terre| Origine | Fichiers éditeurs autorisés sur une archive ouverte |
|---|
Loading...