Crystallization of Parisite. 



551 



generally plane and measurements of sufficient accuracy were 

 obtained to make it clear that these crystals may be referred 

 satisfactorily to the axial elements of aegirite as described by 

 Brogger. As a rule the smaller the crystal the better the 

 quality of its faces ; the best ones were minute needles of clear 

 green color. Larger crystals are dark green to blackish green 

 in color and often occur in subparallel groups, sheaf or rosette 

 forms ; many show fractures more or less healed or extreme 

 bending. 



Twinning on the orthopinacoid is common in larger crystals 

 but is invariably associated with rounding and irregularity of the 

 terminal planes to a degree that entirely precludes measure- 



Fig. 6. 



Fig. 7. 



Figs. 6, 7. Aegirite. 



ments. The basal plane was not observed. The form series 

 as a whole is much more like that of augite than like that 

 described as typical for either aegirite or acmite. None of the 

 forms supposed by Brogger to be peculiar to those species 

 were discovered. On this account and because several of the 

 forms determined have not been recorded for aegirite ; since 

 moreover, this aegirite is shown by the analysis to be nearer 

 to the theoretical aegirite molecule Na.,Fe 2 Si 4 12 than any 

 previously described, it was deemed advisable to calculate the 

 angles of the forms found on the basis of the axial ratio 

 derived from these measurements, and they are accordingly 

 presented in the following table together with the observed 

 angles : 



