sn.nio COMPOUNDS 321 



General description. .Jamr-onitr is a representative of a series 

 of isomorphous lead and silver minerals ; they are generally not well 

 crystallized, and resemble each other so closely that in many cases 

 they are to be distinguished only by chemical analysis. They are 

 not common in occurrence, and are associated with other sulphidrs 

 and arsenides in ore deposits. 



BOURNONITE 



Bournonite. (Cu 2 . Pb) 3 Sb2S 6 ; Cu = 13, Pb = 42.5, Sb = 

 24.7, S = 19.8 ; Orthorhombic ; Type, Didigonal Equatorial ; 

 a:b:c = .9379:1:. 8968; 100 A 110 = 43 10', 001 A 101 = 

 43 43', 001 A Oil ==41 53'; Forms, a (100), b (010), c(001), 

 n (Oil), o (101), m (110) ; Twinning-plane, m ; Cleavage b distinct, 

 a and c less so; H. = 2.5-3; G. = 5.7-5.9; Brittle, fracture 

 uneven; Color and streak gray to iron-black; Luster, metallic. 



B.B. Fuses easily on coal, yielding a white coat of antimony 

 trioxide; on continued heating yields a yellow coat (lead). The 

 residue reduced with soda yields copper buttons or reacts for copper 

 with the fluxes. 



General description. Crystals tabular parallel to the base, 

 with the short prism faces striated parallel to the vertical axis. 

 Often twinned with the prism as the composition face, when repeated 

 forming the characteristic cogwheel-shaped aggregates, as at Kop- 

 nik, Hungary, where it is known as wheel ore. The best crystals 

 are from the Harz, Germany. Also massive, granular, or compact. 



Occurs in the United States in Yavapai County, Arizona ; Mont- 

 gomery County, Arkansas ; and in several localities in Colorado. 

 It is an important ore of lead and copper, but only locally. 



BOULANGERITE 



Boulangerite. Pb 3 Sb 2 S 6 ; Pb = 58.9, Sb =_22.8, S = 18.3 ; 

 Orthorhombic ; Type, Didigonal Equatorial ; & : b : c = .5527 : 1 : 

 .7478 ; Crystal forms, rare ; Brittle, fracture uneven ; H. = 

 2.5-3 ; G. = 5.75-6 ; Color, bluish lead-gray ; Streak, black ; 

 Luster, metallic, dull. 



B.B. The same as zinkenite. 



General description. Crystals very rare, usually fibrous, 

 plumose, granular, or compact. Often with yellow spots of oxide 

 of antimony on the surface. 



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