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SiO2 equilibrium phase diagram. Equilibrium Temperature (T)-Pressure (P) stability of seven phases with the chemical composition SiO2: α-quartz (α-Qz), β-quartz (β-Qz), tridymite (Trd), cristobalite (Crs), coesite (Coe), Stishovite (Sti), and liquid. Notice that only one SiO2 phase is stable at a time, except for the special conditions indicated by the black reaction curves for which two phases are stable. Three phases are stable together only at the special "triple points" (marked by red dots) where three black lines intersect. This confirms that the SiO2 phases are in a one-component system.

The diagram is drawn from experimental data by Bohlen and Boettcher (1982), Zhang and others (1993), and Fei and Bertka (1999).