Mg2SiO4-SiO2 equilibrium phase diagram. Phases at equilibrium for the chemical system Mg2SiO4-SiO2 are shown as a function of chemical composition (weight percent SiO2) and temperature. Areas that have the horizontal line pattern indicate temperatures and compositions for which two phases are in equilibrium. The orange area indicates temperatures and compositions for which a single phase, silicate liquid (magma), is present at equilibrium. The liquid only region is bounded by saturation curves: saturation with the mineral forsterite (Fo), saturation with the mineral protoenstatite (En), saturation with the mineral cristobalite (Crs), and saturation with a second liquid (Liq2). The En and Crs saturation curves meet at a eutectic point, which marks the lowest temperature that liquid can exisit in this system. The Fo and En satuation curves meet at a peritectic point where Fo reacts with the liquid to produce En as the temperature is decreased. Between 1695°C and 2150°C, there is liquid immiscibility for SiO2-rich liquids. This diagram was drawn from data obtained in high temperature experiments by Bowen and Andersen (1914) and by Grieg (1927). The high temperature boundaries of the two-liquid region and the critical point for liquid immiscibility are not well known.