PETRA III Science Seminar | Lamellar amorphization in quartz and its relation to the formation of a rosiaite-structured high-pressure phase of silica

by Christoph Otzen (University of Freiburg)

Tuesday 6 Jun 2023, 14:15 → 15:00 Europe/Berlin

FLASH Seminar Room

Christoph Otzen¹, Hanns-Peter Liermann², Falko Langenhorst^3,4

¹Faculty of Environment and Natural Ressources, Albert Ludwigs University Freiburg, Germany 

²German Electron Synchrotron DESY, Hamburg, Germany

³Institute of Geosciences, Friedrich Schiller Universität Jena, Germany

⁴Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, HI, USA

 

The mineral quartz develops lamellae of glass when exposed to extreme pressure - temperature conditions during asteroid or meteorite impacts (Langenhorst 2002). These so-called planar deformation features (PDFs) provide the most reliable indications of past impact events on the surface of the Earth. Despite the significance of PDFs, the mechanisms leading to their formation has been unclear.

In order to simulate the pressure - time profiles of impacts on longer time scales, we rapidly compressed (0.5 GPa/s) and decompressed single crystals of quartz uniaxially along the crystallographic c axis using the double-sided membrane-driven diamond anvil cell (Sinogeikin et al. 2015). During the compression synchrotron X-ray diffraction images were collected to observe the crystallographic changes. A selection of recovered samples was investigated using the transmission electron microscope (TEM). 

The time-resolved X-ray diffraction images reveal a high-pressure phase transition above 15 GPa. The single crystal-like reflections can be ascribed to a high-pressure phase with a hexagonally closest-packed arrangement of oxygen atoms, while silicon atoms are distributed over octahedral interstices similar to the structure of the mineral rosiaite (PbSb₂O₆). The reflections indicate additionally that the rosiaite-structured phase forms distinct crystallographic orientation relationships to quartz. Upon decompression, the rosiaite-structured phase collapses to glass. This results in the formation of amorphous lamellae as observed in the TEM. Shapes, sizes and crystallographic orientations of the amorphous lamellae resemble remarkably those of PDFs formed in naturally shocked quartz. This means that amorphization of quartz occurs over a large range of time scales during decompression from pressures above approximately 15 GPa. The observations also provide a formation mechanism and an explanation for the crystallographic orientations of the lamellae through formation and collapse of rosiaite-structured silica. 

 

References:

Langenhorst (2002), Bulletin of Geosciences 77, 4, 265 – 282 

Sinogeikin et al. (2015), Review of Scientific Instruments 86, 7, 072209