= Solution
The <fugacity coefficient> $\phi=f/P=0.7$ gives $f=3500\ \mathrm{bar}$. Keep the same solid <thermodynamic activities> and <pressure correction to a mineral reaction> as in part (c), changing only the water <chemical fugacity>:
$$
\boxed{T_{\rm eq}=\frac{98157-0.61(4999)}{164-8.3145\ln(0.7\times5000\times0.6237816764)}=950.38\ \mathrm K=677.23\ ^\circ\mathrm C}.
$$
The lower water <chemical fugacity> makes the dehydrated assemblage more favorable, so the equilibrium <temperature> decreases by about $29.0\ \mathrm K$. This direction is a useful independent check on the logarithm's sign.
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