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1.
The compositions of coexisting orthopyroxene, clinopyroxene and garnet in the CaO-MgO-Al2O3-SiO2 system are fixed at any givenP andT. Reversed hydrothermal experiments over theP/T range 15–40 kb/900°–l,100° C indicate that the garnet composition is nearly constant at Py86Gr14; the Alcontent and Ca/Ca+Mg values of the pyroxenes vary significantly, however:
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2.
Mn3+-bearing piemontites and orthozoisites, Ca2(Al3-pMn3+ p)-(Si2O7/SiO4/O/OH), have been synthesized on the join Cz (p = 0.0)-Pm (p = 3.0) of the system CaO-Al2O3-(MnO·MnO2)-SiO2-H2O atP = 15 kb,T= 800 °C, and \(f_{O_2 } \) of the Mn2O3/MnO2 buffer. Pure Al-Mn3+-piemontites were obtained with 0.5≦p≦1.75, whereas atp=0.25 Mn3+-bearing orthozoisite (thulite) formed as single phase product. The limit of piemontite solid solubility is found near p=1.9 at the above conditions. Withp>1.9, the maximum piemontite coexisted with a new high pressure phase CMS-X1, a Ca-bearing braunite (Mn 0.2 2+ Ca0.8)Mn 6 3+ O8(SiO4), and quartz. Al-Mn3+-piemontite lattice constants (LC),b 0,c 0,V 0, increase with increasingp:
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