MINERALIZERS REMAINING IN CRYSTALLIZED IGNEOUS ROCKS 235 



Rollin S. Chamberlin. 10 But the vast proportion of the gases escape 

 during crystallization. 



While yet dissolved or involved in the magmas, the mineralizers exert 

 an important influence on the fusing point and doubtless tend to lower 

 it very greatly from the high temperatures required for unmineralized 

 melts. Experiment in the laboratory and observation in the field con- 

 vince us that, in general, high silica magmas are richest in dissolved 

 gases, and basic ones less rich. A survey of known occurrences leads to 

 the conclusion that the magmas of the composition of grano-diorite — 

 that is. the ones intermediate between true granites and quartz-diorites 

 and shading into each — are probably the most widespread and greatest 

 contributors of these end-products on crystallizing. True granites are 

 also generous givers, as are the monzonites, intermediate between syenites 

 and diorites. In Broggers classic region around Christiania, high soda 

 rocks have been potent developers of pegmatites 11 and must have been 

 richly charged with mineralizers. As we go down the scale of silica con- 

 tent, mineralizers seem to wane in importance, until we reach the peri- 

 dotites. In them, however, if we are correct in our growing inference 

 that the hydrogen and oxygen in the so-called water or hydroxyl required 

 for serpentinization are of magmatic origin, and that the hydration fol- 

 lowed as an after-effect of crystallization, then the peridotite magmas 

 now represented by serpentine must have been richly charged with the 

 elements of water. 



The general disposition of students of the subject is to consider the 

 mineralizers normal components of deep-seated magmas and to be as 

 much a part of them as the better-known silica and the common bases. 

 Few, if any, who have given the matter thought believe that the involu- 

 tion of sea-water into these molten masses is physically possible. We 

 may admit, however, that, in so far as the upward moving and possibly 

 superheated mass melts into itself and absorbs rocks with minerals such 

 as serpentine or kaolinite, with combined hydrogen and oxygen not easily 

 driven off, the content of mineralizers in the intrusive magma may be 

 increased. 



Eviction or Mineralizers from a crystallizing Magma 



As a general rule, we are all well aware that cooling magmas crystal- 

 lize in largest part into anhydrous minerals, which lack the peculiar 

 elements of the mineralizers. A sweeping statement can not be made, 

 because we do know that hornblendes carry a half per cent or less of 

 hydroxyl; that many micas have hydrogen and fluorine; that apatite, 



