484? On iwo Norwegian Cobalt Ores from the Skutteriider Mine. 



The surfaces g, g' were found on different crystals to form 

 the following angles : — 



1. g:g' =s 58" 30' 4. ^:^-' = 58° 28' 



2.g:g' = 58 32 5.g:g^ = 58 30 



3. g:g' = 58 29 



while in the arsenical iron g: g' = 59° 22'. 



The proportion of cobalt appears therefore, as the deviation 

 amounts to nearly a degree, to have acted in this way on the 

 crystalline form of the mineral. From its properties it may 

 most properly be called cobaltic arsenical iron. 



Second kind. This is characterized by its strong tin lustre, 

 approaching even to that of silver, and still more by its high 

 specific gravity, which = 6'78. It occurs massive, with more 

 or less distinct tessular surfaces of cleavage, and also in single 

 crystals. There can be no doubt that it is the mineral de- 

 scribed some years since by M. Breithaupt, under the name 

 of Tessular pyrites {Tcsseralkies). The analysis gave, 



77'84 arsenic. 

 20-01 cobalt. 



0-69 sulphur. 



1*51 iron, 

 trace of copper. 



100-05 

 which accords pretty accurately with the formula Co As^, ac- 

 cording to which the combination should consist of 



79'26 arsenic. 

 20-74 cobalt. 



100-00 

 if we admit that a quantity of arsenic is remplaced by sulphur 

 and a quantity of cobalt by iron. 



The octahedron is constantly predominating in the crystals 

 of this mineral, with subordinate surfaces of the cube, rhom- 

 bic dodecahedron and icositetrahedron. The last-mentioned 

 surfaces are wanting in none of the crystals. I measured the 

 angles made by two such surfaces with those of the octahe- 

 dron and found 160° 33', whence it results that the parame- 

 ters of the icositetrahedron are as 2 : 1 : 2, therefore just as 

 in the common tin-white cobalt {Speiskobalt). It may bf* 

 called Arsenical Cobalt-pyrites [Arsenikkobaltkies). 



