TENNANTITE. 161 



TENNANTITE. 

 GLAHCE. 



Tennantite. JAM. Syst. Vol. III. p. 563. Man. p. 332 

 Tennantite. PHILL. p. 304. 



Semi-tessular, with inclined faces. Combinations 

 similar to Fig. 158 ... 161 ; often in regular 

 compositions, according to the law of Fig. 164. 

 Cleavage dodecahedron, imperfect Sometimes 

 massive, composition granular ... impalpable. 

 Fracture uneven. 



Lustre metallic. Colour blackish lead-grey. Streak 

 reddish-grey. Opake. 



Brittle. Scratches prismatic and tetrahedral copper- 

 glance, W. PHILL. Sp. Gr. = 4-375, R. PHILL. 



The existence of the regular composition is most easily 

 ascertained by the striae upon the faces of the hexahedron, 

 which are parallel to the edges of combination with one of 

 the tetrahedrons. 



Before the blowpipe Tennantite decrepitates a little, and 

 burns with a blue flame, emitting copious arsenical vapours, 

 and melting at last into a black scoria, which affects the 

 magnetic needle. According to Mr R. PHILLIPS, it con. 

 sistsof 



Copper 45*32. 



Arsenic 11 '84. 



Iron 9-26. 



Sulphur 28-74. 



Silica 5-00. 



It occurs in several of the Cornish copper mines, in yeins 

 traversing granite and clay-slate, and is accompanied by 

 several ores of copper. 



VOL. in. r 



