Polymorphism of feldspars above 10 GPa.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32483171.
- Also identified by DOI 10.1038/s41467-020-16547-4 and PMC identifier 7264230.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Feldspars are rock-forming minerals that make up most of the Earth's crust. Along the mantle geotherm, feldspars are stable at pressures up to 3 GPa and may persist metastably at higher pressures under cold conditions. Previous structural studies of feldspars are limited to ~10 GPa, and have shown that the dominant mechanism of pressure-induced deformation is the tilting of AlO<sub>4</sub> and SiO<sub>4</sub> tetrahedra in a tetrahedral framework. Herein, based on results of in situ single-crystal X-ray diffraction studies up to 27 GPa, we report the discovery of new high-pressure polymorphs of the feldspars anorthite (CaSi<sub>2</sub>Al<sub>2</sub>O<sub>8</sub>), albite (NaAlSi<sub>3</sub>O<sub>8</sub>)<sub>,</sub> and microcline (KAlSi<sub>3</sub>O<sub>8</sub>). The phase transitions are induced by severe tetrahedral distortions, resulting in an increase in the Al and/or Si coordination number. High-pressure phases derived from feldspars could persist at depths corresponding to the Earth upper mantle and could possibly influence the dynamics and fate of cold subducting slabs.