108 B. KOTO 



durino' the preparation of the sections, and the same holds true of the 

 various enclosures in the sericite. It is better therefore to take off by 

 means of a knife a thin flake of this mineral which, when seen under 

 the microscope, shows various interpositions, especially colourless 

 tremolite in slender prisms, resolving at both ends into tufts of fibres. 

 The extinction-direction of tremolite is insignihcant, usually less than 

 10°; the pleochroism not j>erceptible. Minute grains and needles of 

 an almost colourless epidote occur associated Avith the tremolite, 

 within the sericite-aggregate, nuich as in the manner of spicules in 

 sponges. 



A special feature of the minute epidote is its acute rhombic 

 form with sinuating lines along the longer diagonal ; and to a cursory 

 view it looks not unlike small crystals of titanite (pg. 11. h, PL 11), 

 It is the common type of twinned epidote whose structure becomes 

 manifest by different optical orientations in the two halves under polar- 

 ized light. The crystals display vivid chromatic polarization-colours. 



Rhombic dodecahedra of garnet occur together with the epidote. 

 but not with the rutile. The enormous accumulation of the above- 

 mentioned microcrystals causes a dull appearance in the otherwise 

 clear sericite-aggregate. 



In some specimens, as in that from the Kainita-pass in Chichibu, 

 a few long stalky crystals (1-2 centim) were detected whose longi- 

 tudinal terminations split into stiff fibres. They are now^ rusty- 

 brown, although bluish-green wdiere fresh, and their morpholo- 

 gical character resembles that of the primary glaucophane from 

 Ötaki-san in Awa.^^ Taking into account the above-mentioned facts, 

 the writer is rather inclined to consider the tremolite already de- 

 scribed, as having been derived either directly or indirectly from 

 the other minerals such as glaucophane. 



1) loc. cit. 



