Finding The Univariant Curve Using

We discussed the determination of the univariant (in this case three-phase) equilibrium curve in Chapter 8 in terms of finding the locus of P and T for G = 0. This is always 

When this is done for the calculations based on RHF (1978) that we have been doing (Table 13.3), we find that the univariant curve does not coincide with the best available experimental evidence (which in this case is probably the data of Barnes and Ernst, 1963). The calculated curve lies about 30°C to the low-temperature side of the experimentally determined position. If we perform the same calculations using 

Calculate the solubility (i.e., the concentration of SiOaCog)) of quartz and of amorphous silica in water at 25°C. 

602° C, 1 bar is 10 bar. The pyrrhotite in this equilibrium is Feo.gaS, which may be considered as a solid solution composition in the system FeS — Sa. The activity of FeS in this pyrrhotite is 0.46 based on a standard state of pure stoichiometric FeS at the same P and T. The pyrite is pure stoichiometric FeSa. Calculate ArG° for the reaction forming pyrite from pyrrhotite and Sa gas at this P, T. 

A wollastonite-bearing contact metamorphic zone is observed adjacent to a granite which has intruded a quartz-bearing limestone horizon. Heat-flow calculations indicate that the maximum temperature achieved at a given distance from the contact is given by 

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