A new high-pressure phase transition in natural gedrite

Tommy Yong, Craig R. Bina, Gregory J. Finkelstein, Dongzhou Zhang, Przemyslaw Dera*

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

High-pressure diamond-anvil cell synchrotron X-ray diffraction experiments were conducted on single-crystal samples of natural orthoamphibole; gedrite; with composition; (K0.002Na0.394)(Mg2)(Mg1.637Fe2.245Mn0.004Ca0.022Cr0.003Na0.037Al1.052)(Si6.517Al1.483)O22(OH)2. The samples were compressed at 298 K up to a maximum pressure of 27(1) GPa. In this pressure regime, we observed a displacive phase transition between 15.1(7) and 21(1) GPa from the orthorhombic Pnma phase to a new structure with space group P21/m; which is different from the familiar P21/m structure of cummingtonite and retains the (+, +, −, −) I-beam stacking sequence of the orthorhombic structure. The unit cell parameters for the new phase at 21(1) GPa are a = 17.514(3), b = 17.077(1), c = 4.9907(2) Å and β = 92.882(6). The high-pressure P21/m phase is the first amphibole structure to show the existence of four crystallographically distinct silicate double chains. The orthorhombic to monoclinic phase transition is characterized by an increase in the degree of kinking of the double silicate chains and is analogous to displacive phase changes recently reported in orthopyroxenes, highlighting the parallel structural relations and phase transformation behavior of orthorhombic single-and double-chain silicates.

Original languageEnglish (US)
Article number521
JournalCrystals
Volume9
Issue number10
DOIs
StatePublished - Oct 2019

Keywords

  • Amphibole
  • Diamond anvil cell
  • High-pressure
  • Phase transition
  • Single-crystal X-ray diffraction
  • Synchrotron source

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Inorganic Chemistry

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  • Cite this

    Yong, T., Bina, C. R., Finkelstein, G. J., Zhang, D., & Dera, P. (2019). A new high-pressure phase transition in natural gedrite. Crystals, 9(10), [521]. https://doi.org/10.3390/cryst9100521