METASOMATISM. 643 



If this be so, it can not but follow that the minerals precipitated from 

 the solutions in openings will be essentially the same as those produced by 

 the changes within the mineral particles, although their relative proportions 

 may be very different; for it is certain that the changes in the body of the 

 rock are largely accomplished by solution and redeposition, although the 

 material may be deposited very close to the place at which it was taken 

 into solution. 



GROWTH OF LARGE IXDIT1DUALS WITH PRESERVATION OF TEXTURES. 



One of the most distinctive features of metasomatism in the belt of 

 cementation is the growth of large mineral individuals with the preservation 

 or emphasis of original textures and structures. 



The formation of large individuals is a result of the physical-chemical 

 law explained on pages 74-76, under which large individuals form at the 

 expense of smaller ones. In rocks altered 

 by metasomatism in the belt of cementation 

 the more than average growth of certain 

 individuals may be recognized in the very 

 unequal size of the mineral particles and in 

 the enlargement of the old individuals. The 

 general unevenness in the magnitude of 

 mineral particles in rocks altered by meta- 

 somatism in the belt Of Cementation is SO Well Fig. 16.— Clastic quartz penetrated by serpentine. 

 -, i i • -ii i • i After Becker. 



known that the point need not be emphasized. 



While certain individuals may grow to much more than average magnitude, 

 many others break up into very numerous smaller individuals of different 

 kinds; for instance, the change of feldspar to quartz and mica. (See PI. 

 Ill, ,A.) The growth of large individuals at the expense of small ones 

 explains the numerous interpenetrations of minerals in the recrystallized 

 rocks. As a result of the disturbance of equilibrium from any cause, a 

 change may take place. One mineral may grow. At the same time the 

 adjacent mineral may be dissolved. The growth of one in many cases is 

 apparently conditioned by the solution of the other. Cases of this are the 

 growth of magnetite into quartz, and the secondary penetration of needles 

 of actinolite and serpentine into quartz. (See fig. 16.) 



