Erythrite, Co3O8As2 + 8 H2O, As2S5 . 38.4, CoO . 37.6, H2O . 24.0.—
H = 1.5-2.0, G = 2.95.
Color, crimson to peach-red. When crystallized, of pearly lustre, but frequently dull and earthy. Heated in ignition tube gives off water, and color changes to blue or green. Before the Bp. on Ch. in R. F. it emits arsenical fumes and melts to a dark gray globule which with the borax bead reacts for cobalt.
Ores of Copper
Native Copper, Cu.—
H = 2.5-3, G = 8.5-8.9.
Color, copper-red. Lustre, metallic. Occurs usually massive and very arborescent. Before the Bp. on Ch. it fuses, and if the heat is sufficiently high it assumes a bright bluish-green surface; on cooling it is covered with a coat of black oxide. In the borax bead it reacts for copper.
Chalcopyrite, CuFeS2, Cu . 35, Fe . 30, S . 35.—H = 3.5-4, G = 4.1-4.3. Color, brass-yellow, often golden-yellow. Lustre, metallic. Occurs crystallized, but is generally found massive. Is easily scratched with a knife. Heated in an ignition tube decrepitates, and occasionally yields a faint sublimate of sulphur. Before the Bp. on Ch. it blackens, but becomes red again on cooling. Before the Bp. on Ch. with Na2CO3 and KCN it is reduced, and the metals are obtained in separate masses. It reacts with the borax bead for copper and iron.
Copper Glance, Cu2S, Cu . 80, S . 20.—H = 2.5-3.0, G = 5.5-5.8. Color, dark blue to steel-gray. Occurs in compact masses, often very shining. Before the Bp. on Ch. fuses to a globule which boils and emits glowing drops. Sulphur dioxide escapes abundantly, and the outer flame is colored blue. Before the Bp. on Ch. with Na2CO3 yielding a metallic globule.
Tetrahedrite, 4 CuS + Sb2S3.—Frequently contains silver, iron, mercury, and zinc. H = 3.0-4.0, G = 4.5-5. Color, steel-gray to iron-black. Heated in an ignition tube fuses and gives a sublimate of antimonious oxide. When mercury is present this condenses in the upper part of the tube, forming the characteristic mirror. Before the Bp. on Ch. it fuses readily to a metallic globule, emitting dense white fumes; zinc and antimony coatings are deposited on the Ch. After long ignition before the Bp., if the mineral is finely powdered and mixed with Na2CO3 and KCN, the ore is reduced to the metal.