74 PHYSIOGRAPHY. 



Native Platina Native Silver. 



4. It has been chiefly brought from the provinces of Choco and Bar- 

 bacoas in South America, also from Matto-Grosso in Brazil. It has also 

 been found in St. Domingo, and in Siberia. In the mine of Nischne- 

 Taguilsk, (which is also rich in gold, Irid-osmium, Rutile,and even con- 

 tains Diamonds,) several large masses of Native Platina have been found, 

 weighing from seven to fifteen pounds. M. SCHWETZAW describes 

 two varieties in the Russian Platina from Nijnotaguilsk in the govern- 

 ment of Perme. 1. Common Platina. Color platina-grey. Grains 

 angular and bristled, seldom blunt edged ; also in cubical crystals and 

 grouped. Hardness = Hornblende. Malleable. Sp. gr. = 17.. . 1762. 

 Ferruginous Platina. Color darker than the preceding. Surface 

 tarnished, sometimes like meteoric iron. Grains and crystals have the 

 same form as common Native Platina. Hardness = Feldspar, and rather 

 higher. Less malleable than the first. Sp.. g;r. = 14-6 ... 15*7. It is 

 magnetic, and in some grains not only attracts, but repels. It contains a 

 large proportion of iron. 



5. The refractory powers of this metal, and the circumstance that it is 

 not acted upon by the greater part of the chemical re-agents, render it 

 extremely valuable in the construction of philosophical and chemical 

 apparatus. It is used also for covering other metals, for painting on 

 porcelain, for coin, and like gold and silver, for various other purposes. 



NATIVE .SILVER. Silver iMelacone-Metal. 

 Primary form. Cube. 

 Secondary forms. 



1. Cube, with angles truncated. 



2. Regular octahedron. Mexico. 



3. Trapezohedron. Kongsberg. 



Cleavage, none. Fracture, hackly. Surface, the octa- 

 hedron striated in a triangular direction, parallel to its edges 

 of combination with the cube. The remaining faces often 

 rough, but even. 



Lustre metallic. Color silver-white, more or less sub- 

 ' ject to tarnish. Streak shining. 



