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Sect. VIII. 1 



MINERALOGY, 



255 



contain 



useful metals, are commonly termed mineral : it will be 

 sufficient to observe that from decomposition the upper 

 or exposed parts of many do not show the ores in the 

 manner tl;ey occur beneath. Thus, above veins v/herein 

 the ore from which the largest amount of copper is pro- 

 duced, namely the compound of copper, iron, and sulphur 



as 



often found, known by many of our miners as gossan, and 



n 



This is the re- 



sult of a decomposition arising from exposure to atmos- 

 pheric influences of various kinds, and occasionally from 

 otlier influences. It is probable that the sulphur by a union 



uric 



formed 



the copper was attacked and removed, to be 

 dealt with like any other solution of sulphate of copper. 

 And beneath this gossan, or the hack of the lode, as it is 

 often termed, we observe appearances ctrongly reminding 

 us of the common electrotype process for procuring copper 



from a similar solution. 



TI.o pure me 



tal is 



together in chinks and cavities between the main mass 

 of gossan and the body of the undeconiposed copper 



occasiona 



pyrites, mingling, perhaps, 

 part of the former. Sometimes this native copper, as it is 

 called, may retain its metallic character, but at others it 

 becomes converted into an oxide, and this again into a 

 carbonate by the percolation 

 air and carbonic acid. The iron seems in a great mea- 

 sure to have been left behind, and this forms the rusty sub- 

 stance above mentioned. It will be readilv understood that, 



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tlic needful conditions obtaining, other parts of a mineral 



common 



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