4 Description of STERN BERGITE, 



thin sheet-lead, but they do not present any traces of clea- 

 vage. 



The broad faces a are delicately streaked parallel to the 

 edges of combination with h, or in the direction of the long dia- 

 gonals of the rhombic plates. They possess high degrees of 

 lustre. The lustre upon the other faces is not so bright, and they 

 are streaked parallel to their intersections with a ; the faces d 

 less than the rest. A difference of tarnish is likewise often ob- 

 servable. The faces retain their original colour, while all 

 the rest assume a superficial violet-blue tint. 



The lustre is metallic ; colour dark pinchbeck-brown, nearly 

 resembling the colour of magnetic pyrites, only it inclines more 

 to black. 



It affords a black streak. It is very sectile. The laminae 

 are perfectly flexible, and after having been bent, they may be 

 smoothed down again with the nail, like tin-foil or platina leaf. 



The hardness is 1 .0 ... 1 .5, little superior to talc. On ac- 

 count of this low degree of hardness, the mineral leaves traces 

 on paper like black lead, which may be removed by a piece 

 of caoutchouc. The specific gravity of several fragments, amount- 

 ing to 598 milligrammes, I found 4.215. 



Two individuals often join in a regular composition, and pro- 

 duce a twin-crystal ; the axis of revolution being perpendicular, 

 the face of composition parallel, to a face of P -f- GO. Fig. 6. 



Fig. 7- shews a projection of such a twin upon a plane parallel 

 to the face a. The appearance of the twins is, however, not al- 

 ways very regular. Sometimes they are joined by their sides, in 

 a manner somewhat analogous to the twins of felspar found near 

 Carlsbad in Bohemia. 



Generally several crystals are joined in an irregular manner, 

 and implanted together, being fixed to their support with one of 

 their sides, so as to produce rose-like aggregations, and globules 



