Color, iron-black. Lustre, shining and metallic. Pulverized, its powder is black. It is strongly magnetic. Fuses with difficulty before the Bp. on Ch. In borax bead reacts for iron.
Pyrites, FeS2, Fe . 47, S . 53.—
H = 6.0-6.5, G = 4.95-5.20.
Color, brass-yellow. Lustre, metallic. Occurs commonly in cubes. It often contains small quantities of Au, Ag, Cu, As, Co, and Mn. Heated in an ignition tube gives a sublimate of sulphur, the residue becoming magnetic. Before the Bp. on Ch. in O. F. sulphur is burned off and the red oxide remains. This residue may then be examined for iron, etc.
Marcasite (White Iron Pyrites).—Having the same general composition as pyrite, but much lighter in color. Crystals, prismatic. Before the Bp. on Ch. behaves like pyrite.
Pyrrhotite, Fe7S8, Fe . 60.5, S . 39.5.—
H = 3.5-4.5, G = 4.58-4.64.
Color, bronze-yellow. Closely resembles pyrite, but may be distinguished from it by being feebly magnetic. Heated in an ignition tube yields no sublimate. Before the Bp. on Ch. fuses to a magnetic globule, which exhibits a yellowish crystalline structure when fractured.
Mispickel, FeAsS, Fe . 34, As . 46, S . 20.—H = 5.5-6.0, G = 6.0-6.2. Color, silver-white. Lustre, metallic; very brittle. Often associated with it we find small quantities of Co, Ag, and Au. Heated in an ignition tube it first yields a red sublimate of sulphide of arsenic, and then afterward a crystalline sublimate of metallic arsenic. Before the Bp. on Ch. emits dense fumes of arsenic and deposits a coating on the coal; it then fuses to a globule which behaves like pyrrhotite.
Siderite, FeCO3, FeO . 62, CO2 . 38.—H = 3.5-4.5, G = 3.7-3.9. Color, grayish yellow to reddish brown. Lustre, pearly. Crystallizes in rhombohedrons with curved faces; these crystals are distinctly cleavable and massive. Heated in an ignition tube it decrepitates with evolution of carbon dioxide. Before the Bp. on Ch. infusible. Before the Bp. on Ch. with Na2CO3 it fuses to a magnetic mass. With borax bead it reacts for iron and sometimes for manganese.