164 DESCRIPTIONS OF MINERALS. 



associated with cobalt in the sulphides and arsenides. The 

 ores having a metallic lustre vary in specific gravity from 

 6*2 to 7*2; and the color is nearly tin-white or pale steel, 

 gray, inclined to copper-red. The ores without a metallic 

 lustre have a clear red or reddish color, and specific gravity 

 of nearly 3. Cobalt is often present also in arsenopyrite (or 

 mispickel), and sometimes in pyrite. 



The ores of nickel are sulphides, arsenides, arseno-sulph- 

 ides, and an ti mono-sulphides, a sulphate, carbonate, silicates, 

 arsenate ; and the metal is a constituent of several cobalt 

 ores, and also often of pyrrhotite (magnetic pyrites). Specific 

 gravity between 3 and 8 ; hardness of one 3, but mostly be- 

 tween 5 and 6. Those of metallic lustre resemble some cobalt 

 ores ; but they do not give a deep blue color with borax. 



Linnaeite. — Cobalt Sulphide. Cobalt and Nickel Sulphide. 



Isometric. In octahedrons and cubo-octahedrons ; also 

 massive. Color pale steel-gray, tarnishing copper red. Streak 

 blackish gray. H. =5-5. G. =4-8-5. 



Composition. Co 3 S 4 = Sulphur 42 *0, cobalt 5 -80 = 100 ; but 

 with part of the cobalt replaced by nickel ; copper some- 

 times present. Siegenite is a variety containing 30 to 40 j>er 

 cent, of nickel. B.B. on charcoal yields sulphurous odor 

 and a magnetic globule ; often also arsenical fumes. 



Obs. From Sweden, Prussia ; Mine la Motte in Missouri 

 (Siegenite) ; Mineral Hill in Maryland. Sometimes called 

 cobalt pyrites. 



Millerite. — Nickel Sulphide. Capillary Pyrites. 



Rhombohedral. Usually in capillary or needle-like crys" 

 tallizations ; sometimes like wool. Also in columnar crusts 

 and radiated. Color brass-yellow, inclining to bronze-yellow, 

 with often a grav iridescent tarnish. Streak bright. Brittle. 

 H.=3-3-5. "C. =4-6-5 -65. 



Composition. Xi S = Sulphur 35*6, nickel 64*4=100. In 

 the open tube sulphurous fumes. B.B. on charcoal fuses 

 to a globule ; and after roasting, gives, with borax and salt of 

 phosphorus, a violet bead in O.F., which in R.F. becomes 

 gray from reduced metallic nickel. 



