264 Professor Necker o?t Mineralogy considered 



With the blowpipe in the matrass does not decrepitate, nor disengage any 

 volatile substance. In the open tube, gives sulphurous acid without any 

 trace of arsenic, and a white sublimate in microscopic globules, which is sul- 

 phuric acid. Alone on charcoal, after roasting, melts into a grey metallic 

 globule. (Berzelius.) Soluble in nitric acid, and at the same time emitting 

 nitrous gas, and leaving a whitish residuum in the liquid, which is first pink- 

 coloured and after brown. 



*■ First Species — Octahedral Cobalt-pyrites. Sign of the planes r. A regular 

 octohedron, produced by a complete modification by one plane on each of the 

 solid angles of the primitive form. Incidence of r on r 109° 28* 16", from 

 Mussen (Prussia), Vernekinck. 



Var. a, Cuneiform — The terminal angle prolongated in an edge. From 

 Mussen^ idem. 



2. Cuba- octahedral Cobalt-pyrites. — A regular octohedron with all its solid 

 angles truncated by a plane. Sign of the planes P r. Same modification as 

 that of the preceding species, but incomplete. Incidence of P on r 1 25° 1 5' 52". 

 From Mmsen, Vernekinck. 



MODE OF AGGREGATION OP THE INDIVIDUALS OP THIS SUBGENUS. 



In bunches with shining crystalline surface. From Bastnces. 

 II. Subgenus. Glance-cobalt. 



Cebalt-gris, Ha'uy ; part of the hexahedral cobalt-pyrites, or silver-white cobalt 

 of Mohs and Jameson. 



Combination of almost equal volume?; of sulphuret and arseniuret of cobalt. 

 Berzelius's formula, C o S* + C o A s^. 

 Analyses of the glance-cobalt 



of Skutterud (Norway), of Tunaberg (Sweden), 

 by Stromeyer. by Tessaert. 



Arsenic, . . . 43,47 . . . 49,00 



Cobalt, . . . 33,10 . . . 36,66 



Sulphur, . . 20,08 . . . 6,50 



Iron, . . . 3,23 . . . 5,66 



99,88 97,82 



Very lamellar texture, cleavages easy and very shining, parallel to the 

 planes of the cube. 



With the blowpipe in the matrass experiences no alteration ; in the open 

 tube is with difficulty roasted ; gives out arsenious acid merely with a strong 

 heat, and at the same time the smell of sulphurous acid. On charcoal, give 

 out abundant fumes, and fuse after having been some time roasted. Leave 

 at last a brittle white metallic globule (Berz.) 



First Species. — Primitive Glance-cobalt. Sign of the planes P, a cube. In- 

 cidence of P on P 90° /rom Tunaberg. 



Var. a, Triglyphe.—The planes marked with striae in three directions, per- 

 pendicular to one another, /rom Tunaberg. 



2. Octahedral Glance-ccbalt.^See the first species of the first subgenus). 

 From Tunaberg. 



