NOTES ON THE MINERALS OF JAPAN. 233 



42. Opal. 



The most important occurrences of opal in Japan are Bodai 

 in Kaga, the province of Iwashiro, &g. Some of the specimens 

 show irregular double-refracting bands in thin sections. 



Pretty Hyalite spheres of Tateyama in Etchü, about 0.2 cm. 

 in diameter, either loose as sand or cemented together into ag- 

 gregates, were formerly obtainable on the northern shore of a 

 small round lake of hot water, lying about 4 km. to the east of 

 hot-spring hotels. In 1898, I have found only dirty-grey hyalite 

 grains in an ash-like decomposition-product of volcanic rock. 



Silicified wood, usually of coniferous species, is found in 

 tertiary as well as cretaceous deposits of several parts of Hok- 

 kaido, (see Jimbö's General Geological Sketch of Hokkaido, 

 1892) and also at a number of localities in other parts of 

 Japan. 



Diatom-earth forms thick beds in the Tertiaries of Hok- 

 kaido (see the above mentioned work) ; it is also found in Bunco 

 Province, &c. 



43. Manganite. 



Rectangular platy crystals (about 1 cm. long) of manganite, 

 from AsHio in Shimotsuke province, were found associated with 

 copper-pyrite crystals and drusy quartz. Prismatic crystals 

 (about 1 cm. long) of the same mineral came from the Owani 

 mines in Mutsu Province. 



44. Limonite. 



Massive limonite is found to some extent at Yanabara in 

 Mimasaka Province. Limonite in the form of roots of plant has 

 been described by Koto from Takashi in Mikawa Province, 

 and occurs also in several other places. Limonite after pyrite, 



