28 PHYSIOGRAPHY. CLASS n. 



(Pr + a) 3 . (Pr + oc) 5 . ?r + 00. Pr + a>. 

 Morgen stern mine, Freiberg. 



Cleavage, (Pr -f oo) 3 and f r -f oo, imperfect and 

 interrupted. Fracture conchoidal, uneven. Sur- 

 face, Pr and Pr -f- ot> generally streaked parallel 

 to their edges of combination with each other ; 

 the other forms smooth. 



Lustre metallic. Colour iron-black. Streak un- 

 changed. 



Sectile. Hardness = 2-0 ... 2-5, Sp. Gr. = 6-269, 

 a crystal from Przibram. 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpendicu- 

 lar to a face of Pr ; the composition is frequently 

 repeated, either in parallel layers, or contiguous to 

 several parts of the same individual. Thence com- 

 pound masses arise, consisting of alternating la- 

 minae of two or more individuals, as in prismatic 

 Lime-haloide, di-prismatic Lead-baryte, &c., with 

 the forms of which those of the present species 

 agree in a remarkable manner. Massive : compo- 

 sition granular, individuals strongly connected ; 

 fracture uneven. 



OBSERVATIONS. 



1. According to KLAPROTH, it consists of 

 Silver 66-50. 



Antimony 10-00. 



Iron 5-00. 



Sulphur 12-00. 



Copper and Arsenic 0-50. 

 BERZELILS could not discover any antimony by the blow- 



