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The join CaMgSi2O6-Ca2MgSi2O7-CaTiAl2O6 in the system CaO-MgO-Al2O3-TiO2-SiO2 and its bearing on titanpyroxenes

Published online by Cambridge University Press:  05 July 2018

Kosuke Onuma  and
Kenzo Yagi
Kosuke Onuma
Affiliation:
Department of Geology and Mineralogy, Hokkaido University, Sapporo, Japan
Kenzo Yagi
Affiliation:
Department of Geology and Mineralogy, Hokkaido University, Sapporo, Japan
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Summary

The phase equilibrium diagrams of CaMgSi2O6-CaTiAl2O6 with 10, 20, and 30 wt % Ca2MgSi2O7 in the join CaMgSi2O6-Ca2MgSi2O7-CaTiAl2O6 were determined. Six three-phase assemblages, six four-phase assemblages, and two five-phase assemblages (isobaric trivariant, divariant, and univariant) were confirmed. The univariant assemblages are diopsidess+forsterite+åkermanitess + perovskite + liquid and diopsidess+åkermanitess+perovskite+spinel + liquid. Because of the complex solid solutions of diopside and åkermanite the crystallization ceases before invariant assemblages are reached and the final phase assemblage in the diopside-rich region is diopsidess+åkermanitess+perovskite, in the diopside-poor region diopsidess+åkermanitess+perovskite + spinel. Two invariant points, diopsidess+forsterite+åkermanitess+perovskite+spinel+liquid and diopsidess+åkermanitess+anorthite+perovskite+spinel+liquid in the silica-poor region of the system CaO-MgO-Al2O3-TiO2-SiO2 are estimated. The diopside solid solution in this join is discussed with its bearing on the natural titanpyroxenes from alkalic rocks including melilite.

Type
Research Article
Information
Mineralogical Magazine , Volume 38 , Issue 296 , December 1971 , pp. 471 - 480
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1971

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