Abstract
The phase transition between the \(P\bar 1\) and \(I\bar 1\) phases of anorthite has been studied at elevated pressure by single-crystal X-ray diffraction in a diamond-anvil cell. The phase transition is shown to be first-order in character for both end-member anorthite (CaAl2Si2O8) and for an anorthite with a small amount of albite component (NaAlSi3O8) in solid solution. Reversals of the transition across the phase boundary at three other compositions show that the transition pressure (P Tr) increases with increasing albite content. This behaviour is compared with that observed at elevated temperatures, and is analysed in terms of Landau theory.
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Angel, R.J., Redfern, S.A.T. & Ross, N.L. Spontaneous strain below the \(I\bar 1 - P\bar 1\) transition in anorthite at pressure. Phys Chem Minerals 16, 539–544 (1989). https://doi.org/10.1007/BF00202208
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DOI: https://doi.org/10.1007/BF00202208