44 ' '"^'ol. XLli[.. Art. 5.— T. Katô: 



nous silica was deposited at 360-' C, but thoy believe that at this 

 temperature the material is unstable and would soon be converted 

 to quartz. This is the highest temperature at which the gelatinous 

 silica has been synthesized. 



The work of Hein, Leitmcyer and others"^^ leads to the con- 

 clusion that chalcedony is in all cases composed of quartz fibers 

 and that it always results from the crystallization of gelatinous 

 silica either soon after the deposition or at a later «time, and that 

 gelatinous silica may in becoming crystalline either turn into 

 granular quartz or into fibrous quartz, i.e., chalcedony. 



In the case of the ring- ore now in question, it is evident that 

 the crust of chalcedony represents a gelatinous silica transformed 

 to fibrous quartz as its opaline appearance and globular habit under 

 the microscope clearly suggest (PI. Yl., Figs. 1, 3). Consequently, it 

 is highly probable that the copper-tin veins of the Akénobé district 

 were formed chiefly under pneumato-hydatogenetic or hydrothermal 

 conditions, below the critical temperature of water (304- C). 



It is noteworthy that in the Nihonmatsu and Sekiei veins, 

 though a similar ring-ore occurs very commonly, no typical chal- 

 cedony has yet been observed. Tiut under the microscope, the 

 quartz crust corresponding to the chalcedony crust of the Daisen 

 ring-ore is revealed to be an aggregate of indistinct broad fibers, 

 probably representing an advanced stage of transformation of opal 

 to quartz.'^'' 



1) Sumraarizeil in Doelter's " PLindbüch dor MineraU-henue," IM. 2, pp. 165-190, 210-204 

 (1914). 



2) Many examples of transformation of ojjal to chalcedony and qiuxrfz were onumeratcd 

 by p. Cornu and Leitmeyer (" t 'ber analoge Beziehungen zwischen den Mineralien der Opal-, 

 Chalcedon-, der Stilpnosiderit-, H.imatit- und Psiloraelanreihe ") in Zeitschr. f. Chemie u. In- 

 dustrie der Kolloide fKolloid-Zeitschrift), Bd. IV., 1!)09, S. 285-200. 



