Figure 4.04. KAl(Si2O6)-SiO2 (Le-Silica) equilibrium phase diagram with the peritectic point labeled. The peritectic point due to the incongruent melting of sanidine is labeled. It gives the composition (42.2% SiO2) of a liquid that is saturated with both Lct and Sa at 1150°C. Click on the diagram to see the enlarged, interactive version of Figure 4.03 with the peritectic label.
When a Lct-Silica liquid with less than 42.2% SiO2 is cooled, it will start crystallizing leucite when it's temperature reaches the Lct liquidus curve. As the temperature falls further, more Lct will crystallize and the liquid composition will become richer in SiO2 following the liquidus curve. When the temperature reaches the peritectic temperature (1150°C), the leucite present will react with the remaining liquid in the proportions 48% Lct to 52% Liquid to form sanidine crystals. For most bulk compositions, either the Lct will be used up or the Liquid will be used up in this reaction, leaving the other reactant remaining. Answer the following questions to show that you understand which reactant will remain.
Yes. For a bulk composition of 30% SiO2, all the Lct will be consumed in the peritectic reaction producing Sa with Liquid left over. At 1151°C, just above the peritectic temperature, there is 71% liquid and 29% solid (Lct). At 1149°C, just below the peritectic temperature, there is 40% liquid 60% and solid (Sa). You can follow these changes on the Lct-Silica diagram by clicking on the "Show Phase %" and "Coordinates" buttons. No. For a bulk composition of 30% SiO2, all the Lct will be consumed in the peritectic reaction producing Sa with Liquid left over. At 1151°C, just above the peritectic temperature, there is 71% liquid and 29% solid (Lct). At 1149°C, just below the peritectic temperature, there is 40% liquid and 60% solid (Sa). You can follow these changes on the Lct-Silica diagram by clicking on the "Show Phase %" and "Coordinates" buttons.
Yes. For a bulk composition of 10% SiO2, all the Liquid will be consumed in the peritectic reaction producing Sa with Lct left over. At 1151°C, just above the peritectic temperature, there is 24% liquid and 76% solid (Lct). At 1149°C, just below the peritectic temperature, there is 46% Sa and 56% Lct.
No. For a bulk composition of 10% SiO2, all the Liquid will be consumed in the peritectic reaction producing Sa with Lct left over. At 1151°C, just above the peritectic temperature, there is 24% liquid and 76% solid (Lct). At 1149°C, just below the peritectic temperature, there is 46% Sa and 56% Lct.
