KAlSi2O6-SiO2 equilibrium phase diagram. Phases at equilibrium for the chemical system KAlSi2O6-SiO2 are shown as a function of chemical composition (weight percent SiO2) and temperature. 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 four liquidus curves, each of which is a saturation curve for one of the four minerals: leucite (Lct), sanidine (Sa), tridymite (Trd), or cristobalite (Crs). The Sa and Trd liquidus curves meet at a single point called a eutectic point, which marks the lowest temperature that liquid can exisit in this system. The Lct and Sa saturation curves meet at a peritectic point where Lct reacts with the liquid to produce Sa. The Crs and Trd satuation curves meet at the polymorphic (Crs --> Trd) transition temperature (1470°C). Areas that have the horizontal line pattern indicate temperatures and compositions for which two phases are in equilibrium. This diagram was determined experimentally by Schairer and Bowen (1938, 1955) at atmospheric pressure (1 bar).
Wt.% SiO2:
Temperature:
Wt.% Liq:
Liq. Comp:
Wt.% Lct:
Wt.% Sa:
Wt.% Crs:
Wt.% Trd:
