期刊
AMERICAN MINERALOGIST
卷 93, 期 10, 页码 1682-1685出版社
MINERALOGICAL SOC AMER
DOI: 10.2138/am.2008.3019
关键词
Orthopyroxene; isosymmetric phase transition; in-situ X-ray experiments; enstatite-diopside system
High-temperature synchrotron X-ray powder diffraction experiments for the composition of (Ca0.06Mg1.94)Si2O6 have been carried out in the present study to clarify whether orthopyroxene has a transition between low- and high-temperature phases. Our results show that discontinuous changes of unit-cell dimensions and volume occur at 1170 degrees C during both heating and cooling processes and that the space group of Pbca does not change during this reversible phase transition. These facts indicate a first-order and isosymmetric phase transition. This high-temperature phase is thermodynamically distinct from the low-temperature phase, i.e., orthoenstatite in the Mg-rich portion of Mg2Si2O6-CaMgSi2O6 phase diagram, although they have the same space group.
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