484? On two Nor^i^egian Cobalt Ores from the Skutteruder Mine, 
The surfaces g^ f were found on different crystals to form 
the following angles : — 
1, 58*" SO' 4. g\g' = 58° 28' 
2, g:g' = 58 32 S,g:f = 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 ( Tesser alkies) . 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 be 
called Arsenical Cobalt-pyrites [Arsenikkobaltkies), 
