THE ORDER OF CRYSTALLIZATION IN IGNEOUS 
ROCKS 
N. L. BOWEN 
Geophysical Laboratory, Washington, D.C. 
A recent paper in this journal by Mr. Victor Ziegler’ takes the 
form of a criticism of a paper by Bowen on the order of crystalliza- 
tion in igneous rocks. 
Ziegler does not question the statement of Bowen that ‘the 
observation of all the relations of outline of a number of minerals 
in a section of a holocrystalline granular rock leads to a safe 
conclusion only as to the order in which the minerals have ceased 
to crystallize.” The fact that there is agreement on this point is 
worth noting. 
Ziegler does, however, believe that this order of cessation of 
crystallization must be also the order of beginning of crystalliza- 
tion. He says, “the order of cessation of crystallization gives a 
definite clue to the order of beginning of crystallization,” although 
he himself has discussed the crystallization of three-component 
metal systems in which the final crystallization always consists 
in the simultaneous formation of three solid phases (simultaneous 
cessation of crystallization), whatever difference there may be in the 
order of beginning of crystallization which varies with the relative 
proportions. Clearly in those systems the cessation of crystalliza- 
tion gives no clue to the beginning. 
Bowen in the original paper clearly recognized that if the crystal- 
lization of a rock magma is analogous to that of the simple chemical 
systems that have been studied, the final crystallization should 
consist in the formation of a number of solid phases (polycomponent 
eutectic) and that there would be no order of cessation of crystalliza- 
tion. It was suggested that the complications which follow from 
the prevalence of solid solutions among the components of rock 
magmas might, however, give a result which need not be analogous 
* Jour. Geol., XXI, 1913, p. 181. 
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