Letter. High-pressure I2/c-P21/c phase transformation in SrAl2Si2O8 feldspar

In situ, high-pressure single-crystal X‑ray diffraction experiments were performed on a feldspar with composition SrAl Si (space group I2/c). The measurements were performed at 19 different pressures up to 7.9 GPa. The unit-cell parameters and the unit-cell volume show a strong discontinuity at 6.6...

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Bibliographic Details
Published inThe American mineralogist Vol. 96; no. 7; pp. 1182 - 1185
Main Authors Pandolfo, Francesco, Ballaran, Tiziana Boffa, Nestola, Fabrizio, Müller, Monika Koch, Mrosko, Maria, Bruno, Emiliano
Format Journal Article
LanguageEnglish
Published De Gruyter 01.07.2011
Subjects
high pressure
phase transition
single crystal
SrAl2Si2O8 feldspar
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Summary:In situ, high-pressure single-crystal X‑ray diffraction experiments were performed on a feldspar with composition SrAl Si (space group I2/c). The measurements were performed at 19 different pressures up to 7.9 GPa. The unit-cell parameters and the unit-cell volume show a strong discontinuity at 6.6 GPa indicating a first-order phase transition. The systematic absences clearly show that the transition occurs from I2/c to P2 /c space group symmetry, as for the transition recently reported for a feldspar with composition Sr Ca Al Si Our results suggest that the P2 /c phase is softer than the I2/c one. Moreover, within the I2/c symmetry two pressure-volume trends are evident due to a volume softening above 4.2 GPa. The softening did not allow fitting the data to a single equation of state, and only the data up to 3.67 were fitted with a third-order Birch-Murnaghan equation of state. Based on our and previous experimental results we propose a possible composition-pressure stability field for the Sr-rich side along the CaAl Si -SrAl Si join.
ISSN:0003-004X
1945-3027
DOI:10.2138/am.2011.3797