Figure 6.08. Garnet-Biotite Thermometer. Equilibrium compositions of Fe-Mg garnet and Fe-Mg biotite from 550°C to 800°C based on the experiments of Ferry and Spear (1978) and using equation 15-44 of Spear (1993). Tie lines between the coexisiting compositions of biotite and garnet are shown for the full range of Mg/(Mg+Fe) values (garnet X_Mg and biotite X_Mg) for each mineral. Move the slider to change the temperature and, therefore, the K_D. The exchange coefficient K_D = [(Mg/Fe)_Grt/(Mg/Fe)_Bt] is a function of temperature. The tie line shown in red for a particular Mg/(Mg+Fe) value of garnet or biotite can also be changed with a slider.

To see the relationship of this diagram to the AFM diagram of Figure 07 click here.

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