The Join CaMgSi2O6-Ca2MgSi2O7-CaTiAl2O6 in the System CaO-MgO-Al2O3-TiO2-SiO2 and Its Bearing on Titanpyroxenes

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

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.

Mineralogical Magazine; December 1971 v. 38; no. 296; p. 471-480; DOI: 10.1180/minmag.1971.038.296.09
© 1971, The Mineralogical Society
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