Andersen — System Anorthite-Forsterite-Silica. 427 



boundary curves divide the liquidns into three fields each one 

 corresponding to the solid phase, the primary phase, which is 

 the first to separate on cooling of any melt within the field. 



Crystallization curves. — In ternary systems a curve joining 

 all the points which express the successive compositions, and 

 corresponding temperatures, of a melt during its crystallization 



Fig. 4. 



is called the crystallization curve for this melt. A crystalliza- 

 tion curve may begin at any point on the liquidus and it 

 always ends at a quintuple point. In fig. 4, a h m is the crys- 

 tallization curve for a mixture of composition a. For the sake 

 of convenience the behavior of a liquid of initial composi- 

 tion a on cooling is generally described by using the standard 

 phrase that " crystallization proceeds along the curve a b mP 

 This actually means that while crystallization takes place, with 

 separation of one or two solid phases, the successive composi- 



