The remaining solid, therefore, is a mixture of leucite and k-feldspar. The percentages of each solid phase can be determined by the length of the tie line between the compositional points for the two phases and the Lever Rule once again. You can see from the diagram that such an assemblage is forbidden thermodynamically. In the following figure, and the enlargement, the shaded areas represent fields in which a single solid phase exists. Note that at 1254 C carnegieite alters to its low temperature polymorph nepheline.
C begins to crystallize.
D remain, the temperature falls with the precipitation of additional nepheline. The final percentages of the two solid phases is given by a tie line across the nepheline-albite field. Liquid H for this example we will use the enlargement which does not show the X axis making it impossible to determine exact compositions. Remember that as the temperature falls the carnegieite is being converted to nepheline. Note also that in this case only nepheline occurs in our final solid.