PHYSIOGRAPHY. 75 



Native Silver. 



Ductile. Hardness =2-5 . . . 3-0. Sp. gr. =10*4743, 

 HAUY. 



Compound Varieties. Twin-crystals; compound, par- 

 allel to one of the faces of the octahedron. Dentiform, fili- 

 form and capillary shapes, also reticulated, arborescent and 

 in plates. Often the individuals are still discernible, but 

 frequently also their extent can be no longer ascertained. 

 In the latter case, the surface of the dentiform and filiform 

 shapes is longitudinally streaked. Massive : composition 

 rarely observable, fracture hackly. Plates formed in fis- 

 sures, also superficial coatings.- 



1. Native Silver has been divided into common and auriferous Native 

 Silver. It is at present impossible to decide, whether the latter ought to 

 be united as a variety with the former, or whether it forms a species of 

 its own, as we are not yet sufficiently acquainted with all its physical 

 properties, by which alone this question can be decided. Specific grav- 

 ity, and the yellowish color, form -the distinctive marks between them; 

 but as these may arise from the mere juxtaposition of the two metals, 

 they are not alone sufficient for the purpose. 



2. Native Silver is soluble in cold nitric acid, but in the sulphuric acid, 

 only with the assistance of heat. It crystallizes from fusion before the 

 blow-pipe, if the globule is not too lar^e, forming while crystallizing, a 

 single individual, in which the faces of the octahedron, the cube and the 

 dodecahedron, are distinctly seen. 



3. Analysis. 



The common varieties present the silver pure as produced by nature, 

 occasionally alloyed with a small proportion of antimon}^ arsenic, iron, 

 &c. A variety of auriferous Native Silver yielded to KLAPROTH, and 

 another to FORDYCE, the following ingredients: 



Silver - - 36 00 - - - 72-00 



Gold - - - 54-00 - - - 28-00 



4. Native Silver occurs principally in veins, traversing gneiss, clay- 

 slate, and other primitive and transition- rocks. It is accompanied by 

 numerous species of Pyrites, Glance and Blende, as well as by Quartz, 

 Calcareous Spar, &c. The auriferous Native Silver, though it is found 



