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Tol. 66.1 



OKE-DEPOSITION IN LEAD AND ZINC VEINS. 



317 



position of the plane of the specimen with respect to the crj'stal 

 symmetry. The orientation of different groups of figures on a 

 surface thus indicates the different crystal individuals in the 

 specimen. The figures develop best in cubical galena. Banded or 

 ' steel-grained ' ores frequently do not etch without the use of 

 reagents. The blende polishes with a rougher surface, more or less 

 pitted, and grey to brown in colour, while, owing to its greater 

 hardness, it stands up in slight relief above the galena. It does 

 not etch with polishing, and its borders in contact with galena are 



Fig. 9. — Blende, with rough-pitted surface, enclosed in galena : 

 HaVcyn Mine, Flintshire. (Reflected light : x 200.) 





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9 jj 





L 1 



f 



frequently rounded or corroded. The chalcopyrite has a rougher 

 surface and a bright yellow colour. It generally shows good 

 ■crystal outlines, and, like blende, polishes in relief, an effect easily 

 produced by finishing the specimen on parchment or on fairly thick 

 broadcloth. 



Examination of a number of specimens showed that chalcopyrite 

 generally occurs well crystallized and wrapped round by galena or 

 blende (figs. 7 & 8, p. 316). The blende is also generally enclosed 

 in galena (fig. 9). These relations are characteristic, not only of 

 typical British ores, but also of ores from some New South Wales 

 and Queensland localities. The general order of deposition of the 



