4g Vol. XLIIL, Art. 5.-T. Kiitô : 



friiigence, much higher than that of the enclosing quartz ; conse- 

 quently its border appears dark and sharply defined. Double 

 refraction is weak, about the same as, or a little weaker than, in 

 quartz. The basal cleavage is well developed. The character of 

 double refraction along the principal axis is negative. Under the 

 conoscope, a biaxial interference figure appears, and it has been 

 determined by means of thc^ gypsum plate that the mineral is 

 optically positive. The basal section is typically rhombic in shape. 

 These properties coincide exactly with those of topaz. 



The occurrence of the microscopic crystals of topaz in the 

 oro in question is not surprising, because it is suggested by the 

 presence of fluorspar that fluorino-mineralizers have played an 

 important part in the formation of the copper-tin veins of this 

 district. 



(3) The Deposition of Chalcopyrite. 



The deposition of the wolframite-cassiterite ore was succeeded 

 by the deposition of chalcopyrite. This is an important stage of 

 metallization in the vein district now under consideration, but it 

 must be borne in mind that the deposition of chalcopyrite and 

 bornite took place also in the first stage of mineralization, as already 

 stated, although the quantities were insignificant. 



The chalcopyrite of this stage forms not only large veins and 

 patches through the composite vein, but also occurs in the form 

 of streaks, stringers and flecks impregnated in the cassiterite- quartz 

 and quartzose walframite- cassiterite ores. It surrounds and embays 

 all earher minerals, and fills the interstices between the wolframite 

 plates. 



Owing to impregnation with chalcopyrite, the treatment of the 

 tin ores is often rendered very difficult;. Thus very rich copper 



