Summary
The structural changes occurring in the clinopyroxenes with composition Di100, Di90En10 and Di80En20, due to the Ca-Mg substitution in the M2 site, have been studied. Evidence is given that with increasing Mg content a small percentage of the atoms converts from the M2 position to a new M2′ position which is solely occupied by Mg. The maximum conversion of M2 to M2′ found in this study is 7%. The closest parallel to the M2′ geometry is found in the ZnSiO3 pyroxene (C2/c). The presence of this new site causes significant changes in the tetrahedral configuration, because the M2′ atoms are not bonded to 03. The intermediate compositions, Di90En10 and Di80En20, may be thought of as the coexistence of two structural models: diopside and ZnSiO3 pyroxene (C2/c).
Zusammenfassung
Es wurden die strukturellen Änderungen von Klinopyroxenen der Zusammensetzungen Di100, Di90En10 und Di80En20, die durch den Mg-Ersatz für Ca verursacht werden, untersucht. Es zeigt sich, daß mit steigendem Mg-Gehalt ein kleiner Teil der Atome der M2-Position zu einer neuen M2′-Position wechselt; diese wird ausschließlich durch Mg besetzt. Der größte in dieser Arbeit gefundene Übergang von M2 nach M2′ beträgt ca. 7%. Die stärksten Parallelen zur Geometrie um M2′ werden im Pyroxen ZnSiO3 (C2/c) gefunden. Die Besetzung dieser neuen Position verursacht bedeutende Änderungen im Tetraederverband, da die M2′-Atome nicht an O3 gebunden sind. Die Pyroxenstrukturen mit den intermediären Zusammensetzungen Di90En10 und Di80En20 können als Überlagerung zweier Modelle betrachtet werden: Diopsid und ZnSiO3-Pyroxen (C2/c).
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Abbreviations
- En:
-
Enstatite
- Di:
-
Diopside
- Hd:
-
Hedenbergite
- Fs:
-
Ferrosilite
- ClEn:
-
Clinoenstatite
- Di100:
-
pure diopside
- Di90:
-
Di90En10 (mol.-%)
- Di80:
-
Di80En20
- brg:
-
bridging
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Bruno, E., Carbonin, S. & Molin, G. Crystal structures of Ca-rich clinopyroxenes on the CaMgSi2O6-Mg2Si2O6 join. TMPM Tschermaks Petr. Mitt. 29, 223–240 (1982). https://doi.org/10.1007/BF01091794
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DOI: https://doi.org/10.1007/BF01091794