PETROLOGICAL NOTES ON FURTHER ROCK SPECIMENS. 327 



The quartz of the rock shows equally well the cataclastic effects. Often there 

 has been produced in the rock a crude schistosity by the parallel elongation of the 

 crushed portions (cf. Stillwell, p. 134). These effects are rendered more obvious under 

 crossed nicols when the undulose extinction of the alternate bands differentiates one 

 streak from the next. 



Where quartz and felspar are contiguous the crushing has produced new effects. 

 Mynnekitic intergrowths of the two minerals appear, usually in contact with a mosaic 

 of equi-dimensional quartz particles on the side adjacent to this mineral and a 

 well-developed mortar structure on the side abutting the felspar. 



D ' "* 



Fig. 16. 



The pyroxene present is all hypersthene, which shows distinct pleochroism in 

 pinks and greens, with Z green and X pink. The absorption is marked, the formula is 

 Z > X. The appearance of the pyroxene is determined by the degree of cataclasis it 

 has suffered and the extent to which it has undergone metamorphism. The second of 

 these factors determines, to some extent, the amount of hypersthene present in the 

 rock, but it is not the only influencing factor. The amount of original pyroxene is, of 

 course, of importance. This is seen to vary from small quantities, as in Nos. 778, 790, 

 1227, 1254, to considerable amounts as in Nos. 779, 791 , 1226. The degree of granulation 

 appears to affect the readiness with which the pyroxene changes to ilmenite and biotite. 

 The textural effects produced are the lenticular appearance of the larger grains (e.g., 

 No. 787), elongation of the grains (e.g., No. 790), a parallel linearity of the grains (e.g., 

 No. 779) and streaked rows of minute granules (e.g., No. 798). 



