226 K. JiMBö : 



In the tertiary tuffs ofthe Aikawa mines (locality 4), rock- 

 crystal is found in veins of sulphuretted ores ; and in the garnet- 

 rock of Kurodake, the same mineral is found together with vari- 

 ous garnet-crystals, magnetite, pyroxene, &c. At Ohara, ame- 

 thyst occurs in coarse-grained rhyolite ; while at Fujiya the 

 mineral is found with smoky quartz in mountains of granite 

 and other rocks. 



Japanese quartz is often found as Dauphine twins, as for 

 instance the smoky quartzes of the provinces of Omi, Höki and 

 Mino, and the rock-crystals of the provinces Kai and Etchü. 



Twins of rock-crystals on P2 are not very rare at Otomezaka, 

 Takemori, Kawahake, &c. near Köfu ; and on the island Naeu- 

 SHiMA belonging to the Goto group, lying off the coast of Hizen. 

 Those of Narushima usually attain a length of 2 cm., while those 

 from the environs of Köfu are much larger. Two largest speci- 

 mens from the latter, one in the science college and the other in 

 Wada's collection, are nearly 25 cm. long. In the specimens 

 from the region near Köfu, we find clefts parallel to the c axis 

 and perpendicular to the broadest faces of individuals. Two 

 individuals united on P2 are in very rare cases normally deve- 

 loped, instead of being flattened as usual. The small twins of 

 Narushima are quite simple in combination, there being rarely 

 found any trapezohedral face on them. 



The Brazilian twins are quite frequently observed in rock- 

 crystals collected near Köfu, in the Aikawa and Innai mines, at 

 Kurodake in Etchü, at Amagisan in Izu Province and at Katsu- 

 doi in Tosa Province, also in the light-grey quartz from Tano- 

 kamiyama, in the smoky quartz of Mino and of Moraiyama in 

 Shinano Province, and lastly in the amethysts of Ohara and 

 Fujiya. 



