WARREN AND PALACHE. — QUINCY PEGMATITES. 



159 



The forms w(331), (551), (112), and d(131) are new to aegirite 

 although all are known on augite. The habit of the Quincy aegirite 

 crystal is shown by Figures 3 and 4. 



The general mode of occurrence of aegirite in the massive parts of the 

 pegmatites has been previously described and may be briefly summarized 

 here as follows : — It is in almost constant association with the riebeck- 

 ite, either intergrown with it in the body of the crystal, or more com- 



m 



^-L 



Figure 3. 



Figure 4. 



monly about the margins, particularly the ends where it is usually very 

 strongly developed. The vertical axis is commonly parallel to that of the 

 riebeckite, though frequently there is no relation between the positions 

 of the two. This relation to the riebeckite and its common occurrence 

 with quartz indicates a strong preference for the late stages of crystal- 

 lization. Its dominant habit is toward a decided prismatic elongation 

 with a parallel or sub-parallel grouping of separate prisms, as has been 

 noted with regard to crystals in the pockets. When in quartz good 

 prismatic outlines are often noted, but terminations were rarely ob- 

 served in the sections examined. Macroscopically, the color varies 

 from a light, slightly yellowish green to dark, or even blackish green. 

 In thin sections the color is seen to vary greatly even in a single and 

 otherwise optically homogeneous fragment. The usual color is: 



a = Pale to deep green, sometimes with a slight bluish caste : 

 rarely almost colorless, particularly in one part of a crystal. 

 b = Pale yellowish green to almost colorless. 

 c = Pale yellow to pale yellowish green : almost colorless. 



