PYROXENITES OF THE GRENVILLE SERIES 



319 



ows, though the last are more easily distinguished in the larger 

 grains. The lamellae are usually thin, varying from extreme fineness 

 to 0.013 ™"^ in thickness. In sections parallel to the clinopinacoid 

 (010) the extinction angles of the lamellae measured from 38° to 43°, 

 and none were found to extinguish parallel, thus precluding the 

 possibility of an inter- 

 growth of augite and 

 hypersthene. (Fig. 4.) 



Along with the augite 

 there occur as minor con- 

 stituents in varying, usu- 

 ally small, proportions, 

 scapolite, quartz, apatite, 

 brown mica, hornblende, 

 and an opaque iron ore. 



The scapolite has a 

 cloudy, yellowish-gray, 

 fibrous appearance usu- 

 ally, and in places occurs 

 in considerable amount 

 in graphic intergrowth 

 with the augite. This is 

 especially the case near 

 the contact of the pyroxenite with the syenite-gneiss. An analysis of 

 the scapolite by William Hoskins gave the following results : 



Fig. 4. — Section of pyroxenite. A, augite; Ap, 

 apatite inclosing small prisms of zircon ; 5, scapolite; 

 T, titanite. 



SiOo ------- 50.230 



AI2O3 ------- 27.207 



FeO ------- II. 123 



CaO ------- 8.175 



MgO - - - - - - - 1.732 



98.464 



This indicates a high percentage of iron, with a correspondingly 

 low showing of lime, possibly attributable to the altered condition of 

 the material. 



Apatite appears in considerable amount as irregular grains and 

 aggregates. In some cases the pyroxenite and apatite are found in 



