Pseudosections are a type of phase diagram that shows the fields of stability of different equilibrium mineral assemblages for a single bulk-rock composition. Still others show how compositions of phases change under different conditions. Other diagrams (such as the one shown on the right), depict the relationships between a number of compounds having different compositions. Some phase diagrams (those for 1-component diagrams) depict relationships involving multiple phases having the same composition (for example, the relationships between the vapor, liquid and solid forms of H 2O). Standard phase diagrams show how phases or phase assemblages change as a function of temperature, pressure, phase composition, or combinations of these variables. These relationships are governed by the laws of thermodynamics. Standard phase diagrams are graphical representations of the equilibrium relationships between minerals (or others phases). Equilibrium phase relationships between calcite, quartz, wollastonite and CO 2.
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