456 PHYSIOGRAPHY. CLASS n. 



Fundamental form. Hexahedron. Vol. I. Fig. 1. 

 Simple forms. H (P, M) ; 6 (</), Vol. I. Fig. 2. ; 



^ (0, Vol. I. Fig. 19. ; Ii (/), Vol. I. Fig. 27. 

 Char, of Comb. Semi-tessular with parallel faces. 

 Combinations. 1. H. O., Vol. I. Fig. 3. and 4. 



2. H. ^. Fig. 165. 3. O. ~. Fig. 166. 



4. H. O. -- -^. All of them from Tunaberg. 



Cleavage, hexahedron, perfect. Fracture imperfect 

 conchoidal, uneven. Surface, the faces of the 

 hexahedron streaked in three directions perpen- 

 dicular to each other, parallel to the obtuse edges 

 of combination with the pentagonal dodecahedron. 

 The remaining faces smooth. 



Lustre metallic. Colour silver-white, inclining to 

 red. Streak greyish-black. 



Brittle. Hardness = 5-5. Sp. Gr. = 6-298. 



Compound Varieties. Massive : composition gra- 

 nular, generally small, but easily discernible. 



OBSERVATIONS. 



1. According to the analyses by KLAPROTH, TASSAERT, 

 and STROMEYER, the hexahedral Cobalt-pyrites consists of 



Cobalt 44-00 36-00 33-10. 



Arsenic 55-50 49-00 43-46. 



Iron 0-00 5-66 3-23. 



Sulphur 0-50 6-50 20-08. 



The two first of these varieties are from Tunaberg ; the 

 last is from Modum, and is expressed by the formula 

 Co S 4 -f Co As 2 , corresponding to 35-27 of cobalt, 45-27 

 arsenic, and 19-46 sulphur. Before the blowpipe it gives 



