i86 N. L. BOWEN 



Thus the existence of reaction series tends to introduce a fixity 

 in the order of crystalHzation, calcic plagioclase before sodic 

 plagioclase, if at all; forsterite (olivine) before clinoenstatite 

 (pyroxene), if at all; KaSiOj before KaSiOj-fHjO before 

 K,Si03-H,0. 



SERIES WITHIN SERIES 



Both the continuous and discontinuous types of reaction series 

 nciay be much more comphcated than the simple examples chosen 

 for illustration. The continuous reaction series may embrace 

 more than two components, and the reaction between liquid and 

 crystals will then be concerned with the adjustment of the relative 

 concentrations of all of the components. Likewise the discontinu- 

 ous reaction series may consist of any number of members. More 

 than this, any member of a discontinuous reaction series may itself 

 be a continuous reaction series. This case is exempHfied by the 

 system diopside-forsterite-silica.' Here we have the discontinuous 

 reaction series oKvine-cKnopyroxene-silica in which the member 

 cHnopyroxene is itself a continuous reaction series, that is, a soHd 

 solution series. The crystallization of a liquid of this system will 

 illustrate the complexity to which the reaction relation may lead 

 even in this comparatively simple system. The liquid D (Fig. 5) 

 begins to crystallize with separation of the olivine, forsterite. At 

 K the oKvine crystals begin to react with the Kquid to form clino- 

 pyroxene of the composition L, and as the temperature falls the 

 Kquid reacts, not only with the remaining oKvine crystals to make 

 them into pyroxene, but also with the pyroxene crystals already 

 present to make them more calcic. Thus at F the oKvine has 

 been completely changed to pyroxene all of which now has the 

 composition R. In this case, too, lack of opportunity for complete 

 reaction will have an important effect upon the course of the Kquid 

 and the kind of crystals produced from it. Failure of reaction 

 will enrich the Kquid not only in siKca but also in the more calcic 

 pyroxenes. 



CRYSTALLIZATION SERIES IN ROCKS 



A sufficient nimiber of examples of the reaction relation have 

 been given to illustrate the more important aspects of it. More- 

 > N. L. Bowen, Amer Jour. ScL, Vol. XXXVIII (1914), P- 207. 



