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American Mineralogist

Journal of Earth and Planetary Materials

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

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Volume 101, Issue 6


Phase transitions between high- and low-temperature orthopyroxene in the Mg2Si2O6-Fe2Si2O6 system

Shugo Ohi
  • Corresponding author
  • Faculty of Education, Shiga University, Otsu 520-0862, Japan
  • Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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/ Akira Miyake
Published Online: 2016-06-03 | DOI: https://doi.org/10.2138/am-2016-5394


We observed isosymmetric phase transitions of orthopyroxene in the Mg2Si2O6-Fe2Si2O6 system during high-temperature in situ X-ray powder diffraction experiments with a multiple-detector system and a high-temperature strip heater chamber in an atmosphere of Ar plus 1% H2. The transition temperatures we determined for natural orthopyroxenes were 1113–1147, 1120–1139, and around 1200 °C for Fs10, Fs14, and Fs37, respectively, and those for synthetic orthopyroxenes were 1048–1075, 961–1048, and 1037–1148 °C for Fs20, Fs30, and Fs46, respectively. Our experiments showed that the transition from low- to high-temperature orthopyroxene in the Mg2Si2O6-Fe2Si2O6 system occurred at about 1000–1200 °C. We concluded that the stability field of low-temperature orthopyroxene was below 1000 °C and that of high-temperature orthopyroxene was above 1200 °C.

Key words: Orthopyroxene; X-ray powder diffraction; isosymmetric phase transition; enstatite-ferrosilite system

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About the article

Received: 2015-04-28

Accepted: 2016-01-22

Published Online: 2016-06-03

Published in Print: 2016-06-01

Citation Information: American Mineralogist, Volume 101, Issue 6, Pages 1414–1422, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2016-5394.

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© 2016 by Walter de Gruyter Berlin/Boston.

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