128 



B. KOTO 



colour. In spite of its dusky aspect, it displays very vivid, chromatic 

 polarization-colours, unoommon in a partially decomposed felspar. 

 The oblique extinctions upon the faces M and P take place at -41° 

 and -29° to -33° respectively. The positions of hyperbolas seen 

 from M and P are just at the midway between those of hyperbolas of 

 bytownite and anorthite. Along the fissures of the felspar, radiating 

 tufts of stout needles jnay frecpiently be seen with vivid chromntic 

 polarization-colours of green and violet tinges. The angle of extinc- 

 tion is oblique, but in no way do they ever come to total darkness; with 

 hydrochloric acid they gelatinize without difficulty. G. H. Williams^-) 

 seems to have found the same mineral in a orabbro of P>altimore, and 

 the writer agrees with him in considering these tufts to be built up 

 of a zeolite (Scolecite). A very similar gabbro-diorite was recently 

 brought from Mine-oka, in the province of Awa. The felspar of 

 that diorite presents exactly the same ]ia1)itus as that of Chichibu. 

 Tt may be well here to quote, f)r the sake of comparison, the result 

 of the analysis ofthat felspar, which is as follows : — 

 SiO„ 43.59 



ALO, . , 

 Fe,03 . 

 CaO . 

 MgO . 

 K,0 . 

 Na, . . 

 H,0 . 



31.62 



0.90 (Fe wanting) 

 17.25 



0.27 



trace 



1.78 



4.51 



100.42 



Sp. gl-. 2.62 



The crystals of epidote are plentiful iti tlie felspar- substance, 

 especially at the contact between the greenish hornblende and the 



1) Bulletins of the U. S. Geological Survey, No. 28, p. 58. 



