324 



MINERALOGY 



It occurs with pyrargyrite in the same localities and under the 

 same conditions. 



TETRAHEDRITE 



Tetrahedrite. Cu 3 SbS 3 ; Sulphantimonide of copper ; Cu = 

 46.8, Sb = 29.6, S = 23.6 ; Isometric ; Type, Ditesseral Polar ; 

 Common forms, o (111), d (110), n (211) ; Twinning plane, 111 ; 

 Cleavage, none; Brittle, fracture subconchoidal ; H. = 3-4.5; 

 G. = 4.4-5.1 ; Color, lead-gray to iron-black ; Streak, brown 

 to iron-black ; Luster, metallic ; Opaque. 



Tennantite, Cu 3 AsS 3 ; Sulpharsenide of copper. The isomor- 

 phous arsenide is similar in crystallization and appearance and 

 often mixed with the antimonide. 



B.B. Fuses easily in R. F. on coal, yielding a white coat of 

 either Sb 2 O 3 or As2O 3 as the case may be ; in 0. F. yields a sulphur 

 dioxide odor. The coat may contain either lead or zinc oxide if 

 either of these metals is present. Well roasted and reduced with 

 soda yields malleable copper buttons which may be quite white 

 in color from the presence of lead or silver. When mercury is 

 present, the powdered mineral when heated in the closed tube with 

 dry soda will yield a sublimate of small globules of metallic mercury . 

 Decomposed in hot nitric acid with the separation of sulphur and 

 oxide of antimony. 



General description. Crystals are well-developed combina- 

 tions of the plus and minus tetrahedrons, modified by the trigonal 



and tetragonal 

 trisoctahedrons, 

 usually striated 

 or furrowed par- 

 allel to the tet- 

 rahedral edges ; 

 such crystals are 

 found at Kapnik, 

 Hungary, asso- 

 ciated with chal- 

 copyrite, pyrite, 

 and sphalerite. 

 At Clausthal, 

 Harz, the simple 

 trigonal tristet- 



FIG. 405. Tetrahedrite on Dolomite. Clausthal, Harz. rahedron, the 



