H = 3.0-3.5, G = 5.2-5.6.
Color, brass-yellow. Brittle. Before the Bp. on Ch. it fuses to a magnetic, metallic globule. The roasted mineral gives in the borax bead the color reaction characteristic of nickel, and sometimes that of cobalt, which is often associated with it.
Niccolite, NiAs, Ni . 44, As . 56.—
H = 5.0-5.5, G = 7.35-7.67.
Color, pale copper-red. Lustre, metallic. Very brittle. Heated in an ignition tube yields a copious sublimate of arsenious oxide, the residue falling to a greenish powder. Before the Bp. on Ch. fuses to a white brittle globule emitting arsenical fumes. In borax bead gives color characteristic of nickel. Frequently in this mineral a portion of the arsenic is replaced by antimony.
Ores of Silver
Native Silver, Ag.—
H = 2.5-3.0, G = 10.1-11.0.
Color, silver-white. Lustre, metallic. Ductile and malleable. Usually occurs associated with Au, As, Sb, Cu, Fe, etc. Before the Bp. on Ch. easily fuses to a globule which is surrounded with a dark red coating on the coal.
Argentite, Ag2S, Ag . 87.1, S . 12.9.—