194 PHYSIOGRAPHY. 



Fahlerz. 



generally streaked irregularly, parallel to their common edg- 

 es of combination, not rough ; the dodecahedron some- 

 times a little rough. Some varieties are subject to tarnish. 



Lustre metallic. Color steel-grey . . . iron-black. Streak 

 unchanged, sometimes inclining to brown. 



Rather brittle. Hardness = 3-0 ... 4-0. Sp. gr. = 

 4-104, from Cremnitz ; = 4*950 from Kapnik $ =4-798, 

 from Schvvatz-. 



Oompound Varieties. Twin-crystals : face of compo- 

 sition parallel to a face of the octahedron ; the individuals 

 continued beyond the face of composition. 



Fig. 181. 



Dillenburg. 



Massive : composition granular, of various sizes of indi- 

 viduals, strongly connected, and often impalpable ; fracture 

 uneven. 



1. Schwarzerz has been distinguished as a subspecies under Fahlerz. 

 but differs only in having a deeper black color, and a more conchoida! 

 fracture. 



The varieties of the present species differ somewhat in their behavior 

 before the blow-pipe, arising chiefly, it may be concluded, from acci- 

 dental mixtures, depending upon the substances with which they occur 

 associated. Some jyeld arsenic when roasted, others antimony, and the 

 residue melt in different ways. After roasting, (hey yield a globule of 

 copper. 



