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LEAD ORES, 



277 



NATIVE LEAD. 



A rare mineral, occurring in thin laminae or globules 

 Gr=s»ll '35. Said to have been seen in the lava of Madeira » 

 at Alston in Cumberland with galena ; in the county oi 

 Kerry, Ireland ; and in an argillaceous rock at Carthagena. 



galena. — Sulphuret of Lead. 



Monometric. Cleavage cubic, eminent. Occurs under 

 ft he form of the cube and its secondaries. 



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Cleavage cubic, perfect, and very easily obtained. Also 

 coarse or fine granular ; rarely fibrous. 



Color and streak lead gray. Luster shining metallic. 

 Fragile. Hs=2*5. Gr=7.5— 7-7. 



Composition : when pure, lead 86*55, sulphur 13'45. 

 Often contains some sulphuret of silver, and is then called 

 argentiferous galena, and at times sulphuret of zinc is pres- 

 ent. Before the blowpipe on charcoal, it decrepitates un- 

 less heated with caution, and fuses, giving off sulphur, and 

 finally yields a globule of lead. 



Dif. Galena resembles some silver and copper ores in 

 color, but its cubical cleavage, or granular structure when 

 massive, will usually distinguish it. Its sulphur fumes ob- 

 tained before the blowpipe prove it to be a sulphuret ; and 

 the lead reaction before the blowpipe show it to be a lead 

 ore. 



Obs. Galena occurs in granite, limestone, argillaceous 

 and sandstone rocks, and is often associated with ores of 

 zinc, silver and copper. Quartz, heavy spar, or carbonate 

 of lime, is generally the gangue of the ore ; also at times 

 fluor spar. vThe rich lead mines of Derbyshire and the\^X 

 northern districts of England, occur in mountain limestone ; 

 and the same rock contains the valuable deposits of Bleiberg 



Where has native lead been found 1 What is the structure of galena 

 its physical characters ? its composition and blowpipe characters 

 How is it distinguished from silver and copper ores 1 Where does it 



