Sl'UMIIDKS, AHSKXIDKS, ANTl.NK >.\l 1 >KS 



L'lIU 



B.B. Fuses easily on coal in the (). F., yielding S( ) 2 fumes and 

 :i yellow oxide of lead coat, which is often quite white with lead 

 carbonate or sulphate. In R. F., especially when mixed with soda, 

 is reduced to malleable lead. The soda fusion, when placed on a 

 silver surface and moistened, leaves a black stain (Sj. Dissolves 

 in nitric acid, forming insoluble white lead sulphate (PbSO,i). 



General description. Crystals are usually cubic or combina- 

 tion of the cube and the octahedron, less often the rhombic dodeca- 

 hedron; the simple octahedral habit is rare. Other forms occur 



FIG. 398. Galena Crystals. Bavaria. 



which at times give the crystals a rounded appearance; cube faces 

 are often vicinal. Twins after the spinel law are flattened, as is 

 usual with twins of this class. Cleavage is cubical with brilliant 

 surfaces, and in some cases striated from polysynthetic twin*- 

 ning ; in rare exceptions, as at Lancaster, Pennsylvania, and Nord- 

 marken, Sweden, the cleavage is octahedral ; such specimens have 

 always been found to contain bismuth. Massive, granular, and 

 disseminated varieties are common, but fibrous and plumose speci- 

 mens are rare. Galena contains as impurities zinc, copper, cad- 

 mium, bismuth, arsenic, and antimony, possibly as sulphides; 

 also gold and silver; often the silver value is greater than that 

 of lead, when it constitutes a true silver ore. 



Galena occurs both as a primary and secondary mineral, but by 

 far the most important commercially are the secondary vein de- 

 posits or those filling cavities in limestone formations, where it is 

 associated with sphalerite and chalcopyrite. The gangue of such 



