100 Vol. XLIIL, Art. 6. - S. Tsuboi : 



Augite is a greenish, high double-refracting one, traversed by 

 characteristic cleavage Unes parallel to (110) and often twinned on 

 (100). It is noteworthy for its pleochroism. Pleochroisra is 

 noticeable in thicker sections, especially in those which extinguish 

 nearly straight. It is as follows : — 



A'' yellowish greeu 



Z' deep gi'een 



" Alisorption Z' > A'^' 



Here, X^ and Z^ respectively den, te the vibration directions 

 of the faster and the slower rays in section. 



The ol3served refractive indices for sodium light of this unusual 

 augite are given below. For comparison, those of the minerals 

 from other localities which have like optical properties are cited in 

 parallel columns. 



Optical plane 1| (010). 



Augite sometimes includes small crystals of plagioclase. 



Magnetite is found as an accessory ingredient in sabhedral 

 crystals and apatite is as usual in small needles witli characteristic 

 negative elongation. 



The interstices of the component minerals are often filled with 

 a colourless salic matter with somewhat lower refractive indices 



1) Here a' and 7' respectively denote the observed minimum and maximum refractive 

 iudice.s. 



