Fig. 2.

Pressure–temperature diagram showing the limits on stability of forsterite and antigorite in the MgO–SiO₂–H₂O system (solid lines) and part of an isochemical P–T section showing the equilibrium conversion of olivine (fo₉₂) to Mg–Fe serpentine (dashed lines). The olivine (fo₉₂) composition (CaO:0.02–FeO:8.11–MnO:0.12–MgO:50.37–SiO₂:40.34) is the average of eight analyses of kimberlitic olivine grains (Table 1, Kamenetsky et al. 2004), and P–T range of equilibrium conversion to serpentine was calculated with Perple_X (Connolly 2005) assuming H₂O saturation. (Question mark) indicates uncertainty of the lower thermal boundary of metastable conversion of olivine to serpentine