THE CRYSTALLIZATION OF IGNEOUS ROCK 



171 



which frequently cause large-scale changes and very profound 

 effects, especially in the way of mineralization. 



Another illustration of the same process is shown in Figures 

 2 and 3. In this case the rock, a diorite from Newfoundland, is 

 self-injected in the same manner, but the effects are more profound. 

 The original f erromagnesian mineral has been wholly converted to a 



Fig. 1 



Fig. 2 



Fig. I. — Photomicrograph of deuterized granite, Fort Ann, New York. Nicols 

 crossed, magnification 20 diameters. The earUer feldspar is orthoclase, which has been 

 heavily injected with end-stage consolidation products consisting of quartz and albite 

 (.4). These products are both interstitial, and injected through the rock, on a micro- 

 scopic scale. The black grains are quartz at the position of extinction. A crystal of 

 orthorhombic pyroxene (P) has been converted to serpentine by the same agents and 

 during the last stages of crystallization. 



Fig. 2. — Photomicrograph of diorite from Newfoundland. Nicols crossed, magnifi- 

 cation 20 diameters. Coarsely granitoid in texture; the single large crystal (dark 

 gray) is an earlier plagioclase feldspar of andesine composition thoroughly injected 

 with end-stage quartz and albite. Connected with this stage and because of changes 

 in equilibrium, together with hydration effects, the ferromagnesian mineral {A) has 

 been converted to an interlacing mat of actinolite needles. 



complex of matted actinolite needles and the plagioclase, otherwise 

 quite fresh and unaltered, has been thoroughly injected and soaked 

 with quartz and albite ; changes obviously connected with end-stage 

 emanation products of a dioritic magma. 



Even in more basic rocks such phenomena are common where 

 the mass is of sufficient extent to have permitted more or less 

 crystallization-differentiation. In the diabase which forms the 



