204 ART. 3. — E. KOTO : 



by reflected light can afford a clue in discriminating the sulphide 

 from pyrite. Moreover, the presence of pyrrhotite is the sign of 

 eruptivity, while pyrogenic pyrite is a product of post-volcanic 

 activity. A rock similar in minéralogie composition to the well- 

 known pyrrhotite-bearing cor dierite- gneiss of plutonic origin found 

 at Bodenmais, Bavaria, is, therefore, represented in the recent lava 

 of Sakura-jima. 



From the mode of the constant association of pyrrhotite and 

 cordierite, the writer surmises a peculiar relation between them. 

 In the grayish porcelaneous éjecta thrown up in a temporary 

 eruption of xisama on the 13th of December, 1912, we find grayish 

 blue stripes, which under the microscope (PI. XXII. Fig. 8) are seen 

 to consist of an aggregate of cordierite rectangles cemented by 

 pyrrhotite — a mass serving for the matrix of the resorption-relic 

 of the microphenocryst of a basic plagioclase (an). The cementing 

 pyrrhotite sustains the same relation to the enclosed cordierite 

 microcrystals, as the xenomorphic chalcopyrite to the idiomor- 

 phic ironpyrite of high crystallinity in ordinary orebodies. Both the 

 pyrrhotite and cordierite are primary secretionary products of a 

 basic andésite magma, and any explanation on the close associa- 

 tion of iron and copper pyrites will help in the elucidation of the 

 genetic relation of the two minerals in our ceramicites. 



The neovolcanic cordierite is associated with andésites and 

 liparites, but not with basalt, so far as the writer is aware of. 

 The cordierite-bearing éjecta are direct oflsprings of the former, 

 wliile in the latter (plagioliparite) they occur as cognate xenoliths 

 (Haeker). 



Exhaustive study of cordierite is out of place here. The 

 writer can only say that idiomorpliic crystals, save those rectangular 

 microcrystals, are not observed. Trillings, whose formation is sup- 



