Subsurface Laboratory Methods 



167 



In general, statistical diagrams of quartz show (fig. 69) either iso- 

 lated maxima or a distribution of axes in bands that may or may not 

 contain maxima. Fairbairn,^^ has an illustration in his book that shows 

 the types of quartz diagrams possible from thin sections cut normal to the 

 reference axes a, b, and c. 



1 ..^^b^.iS^ 



Figure 64. Looking south along b axis of a tight, slightly overturned fold in bedded, 



schistose quartzite. 



The micas (biotite, muscovite) ordinarily show a complete or partial 

 girdle (fig. 70) around b parallel to the a~c plane with a maximum at c. 



Figure 71 is a schematic drawing of the fold shown in figure 64. 

 This fold is in a schistose, white quartzite, in which parallel muscovite 

 flakes produce the schistosity. The simplified petrofabric diagrams super- 



^' Fairbaim, H. W., Structural Petrology of Deformed Rocks, p. 8, Cambridge, Mass., Addison-Wesley 

 Press, 1942. 



