Fo-En-Qz PT Diagram
T (°C):
P (GPa):

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Fo-En-Qz X Diagram
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Bulk Composition
Wt.% SiO2: 25.0

Equilibrium Assemblage
Wt.% Mineral:
Wt.% Mineral:
± H2O


Mg2SiO4 - SiO2 diagrams projected from H2O.

The diagram on the left shows the pressure-temperature stabilities of Forsterite (Fo), Antigorite (Atg), Enstatite (En), Talc (Tc), Quartz (Qz) and Water (H2O) based on experimental studies of chemical reactions among the minerals. Water is included in the experiments so that pressure P(total) = P (H2O). Mouseover the T-P diagram to see mineral assemblage information for a Mg2SiO4-SiO2 composition of 25 wt.% SiO2.

The diagram on the right shows the compositions of the minerals as projected from H2O onto the Mg2SiO4-SiO2 2-component line. H2O (supercritical water) is a phase in all equilibrium assemblages. Move the slider to select an Mg2SiO4-SiO2 bulk composition, then mouseover the T-P diagram to see the assemblage changes. To change the T-P diagram on the left to a mineral assemblage diagram (MAD) based on the selected bulk composition, click on the "Show MAD" button. Remember that water should be added to all assemblages.

The data used to calculate the reaction curves were taken from the thermodynamic model dataset SPaC (version 2015) developed originally by Spear and Cheney (1989) using a standard state of formation from the elements at 298.15 K and 1 bar.