Andersen — Sy stein Anorthite-Forsterite-Silica. 431 



tic but an alteration point, the qualities of which will be 

 explained below. With the exception of this point o and the 

 curve o rn all points and curves of this type have the same 

 general qualities as the corresponding points and curves of 



.Examples of crystallization. — To explain the relations of 

 the point o and the curve o m we follow some crystallization 



Fig. 6. 



C 



curves, starting from points within the field of A. From a 

 melt of composition a the solid phase A crystallizes between 

 a and b. From b to o A and D crystallize together, but as the 

 total composition of the solid separated between a and o is 

 given by the point a' there must be liquid left when o is 

 reached. As now the crystallization curve always has to end 

 at a quintuple point, it is easy to see that in the present case 

 the final solidification takes place at o. A continuation of the 

 crystallization to m would mean that the final solid consisted 



