Figure 25.7 is a ternary ACF compatibility diagram for medium-grade metamorphosed basalts. H2O is perfectly mobile, and the parageneses can be treated as three-component systems. The shaded area represents the typical range of metabasalt compositions. Discuss each paragenesis for the shaded range in terms of the full phase rule and Goldschmidt’s mineralogical phase rule. What variables are associated with when = and when <   F C C?
Figure 25.7 is a ternary ACF compatibility diagram for medium-grade metamorphosed basalts. H2O is perfectly mobile, and the parageneses can be treated as three-component systems. The shaded area represents the typical range of metabasalt compositions. Discuss each paragenesis for the shaded range in terms of the full phase rule and Goldschmidt’s mineralogical phase rule. What variables are associated with F when  = C and when  < C?