ORDER X. PRISMATIC NICKEL-PYRITES. 447 



Traite, T. III. p. 513. Tabl. comp. p. 84. Traite, 

 2de Ed. T. III. p. 417- 



Fundamental form. Scalene four-sided pyramid 



of unknown dimensions. Vol. 1. Fig. 9. 

 Simple forms and the character of combination not 

 satisfactorily ascertained. The latter seems to be 

 nearly allied to those of prismatic Iron-pyrites, 

 of diprismatic Lead-bary te, &c. particularly in re- 

 gard to the regular compositions in which their 

 individuals occur. 

 Cleavage unknown, imperfect. Fracture small 



conchoidal, uneven. Surface smooth. 

 Lustre metallic. Colour copper-red. Streak pale 



brownish-black. 



Brittle. Hardness = 5-0 ... 5-5. Sp. Gr. =7-655. 

 Compound Varieties. Reniform : composition 

 columnar, generally impalpable. Massive : com- 

 position granular, the individuals being small, and 

 strongly connected. Fracture uneven. 



OBSERVATIONS. 



1. According to two analyses, one by STROMEYER, and 

 another by PFAFF, the prismatic Nickel-pyrites consists of 

 Nickel 44-206 48-90. 



with a little Cobalt. 



Arsenic 54-726 46-42. 



Iron 0-337 0-34. 



Lead 0-320 0-56. 



Sulphur 0-401 0-80. 



It is represented by the chemical formula Ni As, which 

 corresponds to 44-01 of nickel and 55-99 of arsenic. Be- 

 fore the blowpipe it melts upon charcoal, and emits an 

 arsenical smell. The remaining metallic bead is white 



