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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2017: 2.31

SCImago Journal Rank (SJR) 2017: 1.440
Source Normalized Impact per Paper (SNIP) 2017: 1.059

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1945-3027
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Volume 89, Issue 10

Issues

High-pressure phase transitions in Ca0.2Sr0.8Al2Si2O8feldspar

Fabrizio Nestola
  • Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany
  • Dipartimento di Scienze Mineralogiche e Petrologiche, Via Valperga Caluso 35, I-10125 Torino, Italy
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/ Tiziana Boffa Ballaran / Piera Benna
  • Dipartimento di Scienze Mineralogiche e Petrologiche, Via Valperga Caluso 35, I-10125 Torino, Italy
  • Istituto di Geoscienze e Georisorse, CNR, Sezione di Torino, Via Accademia delle Scienze 5, I-10123 Torino, Italy
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/ Mario Tribaudino
  • Dipartimento di Scienze Mineralogiche e Petrologiche, Via Valperga Caluso 35, I-10125 Torino, Italy
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/ Emiliano Bruno
  • Dipartimento di Scienze Mineralogiche e Petrologiche, Via Valperga Caluso 35, I-10125 Torino, Italy
  • Istituto di Geoscienze e Georisorse, CNR, Sezione di Torino, Via Accademia delle Scienze 5, I-10123 Torino, Italy
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Published Online: 2015-03-28 | DOI: https://doi.org/10.2138/am-2004-1015

Abstract

A synthetic feldspar of composition Ca0.2Sr0.8Al2Si2O8 (An20SrF80) (space group I1̄ at room condition, Qod = 0.88) was investigated using in situ high-pressure single-crystal X-ray diffraction. Unitcell parameters were measured as a function of pressure to 7.7 GPa at room T. Two reversible phase transitions were observed in the investigated pressure range. A first-order triclinic I1̄ to monoclinic I2/c phase transition was observed at P ∼ 4.3 GPa. Several cycles through the transformation were made to constrain the hysteresis (∼0.3 GPa). The discontinuous character of the transition is especially noticeable in the behavior of the γ angle, which increases from 90.55° to 91.04° before Ptr. The Murnaghan EoS parameters obtained for the volume are: V0 = 1393.97(6) Å3, K0 = 88.7(5) GPa, K' = 1.3(3) for the triclinic I1̄ phase and V0 = 1396.9(1) Å3, K0 = 89.4(9) GPa, K' = -1.7(6) for the monoclinic I2/c phase whose high-P behavior appears, therefore, linear in the pressure range of its stability. The axial compressibility scheme is βa > βc > βb for both phases, in good agreement with previous observations for other feldspars. A similar displacive ferroelastic I1̄-I2/c phase transition was observed for the same sample with increasing temperature. At P ∼ 7.3 GPa a large discontinuity in the unit-cell parameters indicates a further transition from monoclinic I2/c phase to monoclinic-II phase. This transformation is strongly first order with a volume change of about 1.7%.

About the article

Received: 2003-09-04

Accepted: 2004-03-09

Published Online: 2015-03-28

Published in Print: 2004-10-01


Citation Information: American Mineralogist, Volume 89, Issue 10, Pages 1474–1479, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2004-1015.

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© 2015 by Walter de Gruyter Berlin/Boston.

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