THE CRYSTALLIZATION OF IGNEOUS ROCK 



175 



be connected with late-stage crystallization; the coarsely micro- 

 graphic matrix, which has the general characteristics of a quartz- 

 feldspar eutectic, the chloritization of the biotite and " actinolitiza- 

 tion" of the hornblende (or the uralitization of an original pyroxene) 

 are all products of the activity of a solution-residuum formed in 

 relatively large quantities during the selective crystallization of a 

 much more basic magma. Figures No. 8 and 9 are illustrative 



Fig. 7 



Fig. 8 



Fig. 7. — Photomicrograph of norite from the Creighton Mine, Sudbury, Ontario. 

 Nicols crossed, magnification 20 diameters. Swamped in end-stage quartz {Q) which 

 in places had flooded the rock. The original orthorhombic pyroxene almost wholly 

 uralitized and reorganized; considerable soda has been added in the processes so that 

 in places a blue amphibole of about the quality of glaucophane has been formed, grading 

 into the commoner green actinolitic hornblende. This rock has been more profoundly 

 affected than the one shown in Figure 6. 



Fig. 8. — Photomicrograph of micropegmatite from the acid margin of the nickel 

 eruptive, Sudbury district, Ontario. Nicols crossed, magnification 20 diameters. 

 Showing quartz in large crystal units {Q) , albitized feldspar {F) , and spherulitic chlorite 

 (C), derived from biotite. The character of the rock is dependent on end-stage 

 crystallization processes. 



of this particular phase of late-stage crystallization. Both are 

 "micropegmatites" from the Sudbury region, taken from the acid 

 border of the nickel eruptive. 



Figure 8 shows the larger crystal units of quartz flooding 

 earlier feldspar, which has been albitized, and spherulitic chlorite, 

 derived from biotite. Figure 9 shows the coarsely micrographic 

 intergrowth of feldspar and quartz; the ferromagnesians have 



