Abstract
We used transmission electron microscopy (TEM) to understand microstructural changes accompanying the reversible I1̄-P1̄ phase transition in Ca-rich plagioclase as a function of Na content. The transition produces c- and d-type domains that have P1̄ symmetries, and the symmetries of domain walls are I1̄. Based on diffractograms and contrast differences of high-resolution TEM (HRTEM) images, we infer that structural differences occur on a scale of tens of nanometers, giving rise to structural fluctuations. These variations can be followed on a nanometer scale using HRTEM images. We propose a model with a body-centered A1-Si framework and single Ca sites for the I1̄ domains. The P1̄ domains of anorthite with high A1-Si ordering are homogeneous. In contrast, structural fluctuations occur in both anorthite with lower A1-Si ordering and in Na-bearing plagioclase. The magnitudes of the fluctuations decrease with increases in Na content.
Original language | English (US) |
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Pages (from-to) | 1080-1086 |
Number of pages | 7 |
Journal | American Mineralogist |
Volume | 92 |
Issue number | 7 |
DOIs | |
State | Published - Jul 1 2007 |
Keywords
- Ca-rich plagioclase
- HRTEM
- I1̄-P1̄ phase transition
- Structural fluctuations
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology