as a Branch of Natural Hiatory, S^c. 205 



3. Dodecahedral Glance-cobalt. — Sign of the planes e. A pentagonal dodeca. 

 hedron, twelve pentagonal planes produced by a complete and unsymmetric 

 modification • of one plane (instead of two) on all the edges of the primary 

 form. Incidence of e on e and e' 126^°, and 113^' from Tunaberg. 



4. Icosahedral Glance-cobalt. — Sign of the planes ed, a. solid with twenty tri- 

 angular planes, of which, in the normal state, eight (d) are equilateral triangles, 

 and twelve (e) are isosceles triangles. Combination of two incomplete modi- 

 fications, one of one plane on all the solid angles, and the other an unsymmetric 

 one of one plane (instead of two) on all the edges of the primary form, which 

 is totally intercepted by such a combination of modifications. Incidence of e 

 on d 140° 4C' r- 



6. Cubo-icosahedrai Glance-cobalt. — Sign of the planes M.Ted. The same 

 combination of modification as the preceding species, but not intercepting en- 

 tirely the primitive form, and leaving the common base of each two adjacent 

 isosceles triangles replaced by a plane. 

 Incidence of e on P 153° 26' 5". 

 done 140M6'7". 

 rfonM125" 15'52''. 

 d on P 152° ly 52'\ from Tunaberg. 



III. Subgenus. Silver-white cobalt. 



Weisser speiss kobalt of Werner ; Cobalt arsenical blanc argentin (Haiiy). A 

 part of the hexaedral cobalt-pgrites and of the silver-white cobalt of Mohs and 

 Jameson. 



Mixture of glan;i5-cobalt with arsenical pyrites, or of sulphuret and arseni- 

 uret of cobalt with sulphuret and arseniuret of iron. Berzelius*s formula. 

 CoS* + CoAS2, FeS* + Fe AS^. 



Colour, silver-white ; texture more compact than lamellar ; external lustre 

 less vivid than that of the glance-cobalt. Before the blowpipe disengages 

 much arsenical fumes with a strong smell of garlic, and leaves as a residue a 

 brittle, white metallic globule. 



First Species. — Primitive silver-white Cobalts* A cube. Sign of the planes 

 P. Their mutual incidence 90°. 



MODE OP AGGREGATION OP THE MOLECULAR INDIVIDUALS OP THE 

 WHOLE GENUS. 



In compact masses. 



• We call uru3/mmetric modificati(Mi what Mohs calls in this case semi-tessular, when the half of 

 the planes which ought to exist according to the law of symmetry are suppressed. 



