Part 9 (1/2)

H = 2.0-2.5, G = 7.20-7.36.

Color, blackish lead-gray. l.u.s.tre, metallic. Very sectile. Before the Bp. on Ch. in O. F. intumesces with evolution of sulphur dioxide, finally yielding a metallic globule of Ag.

~Pyrargyrite~, Ag_{3}SbS_{3}, Ag . 59.8, Sb . 22.5, S . 17.7.--H = 2.5, G = 5.77-5.86. Color, black to dark cochineal-red. l.u.s.tre, metallic, adamantine. In an ignition tube it yields on continued heating a sublimate of antimony sulphide. Before the Bp. on Ch. it gives a coating of antimony trioxide. Before the Bp. on Ch. with Na_{2}CO_{3} is reduced to metallic silver.

~Proust.i.te~, Ag_{3}S_{3}As, Ag . 65.5, As . 15.1, S . 19.4.--H = 2.0-2.5, G = 5.57-5.64. Color, light red. l.u.s.tre, splendent, adamantine. Before the Bp. on Ch. it behaves like pyrargyrite, save that it gives off a.r.s.enical fumes instead of antimonious oxide.

~Stephanite~, Ag_{5}S_{4}Sb, Ag . 68.5, Sb . 15.3, S . 16.2.--H = 2.0-2.5, G = 6.2-6.3. Color, iron-black to blackish gray. l.u.s.tre, metallic. Very brittle and fragile. In an ignition tube it decrepitates, fuses, and finally yields a slight sublimate of antimony trisulphide. Before the Bp. on Ch. gives a coating of antimonious oxide. Before the Bp. on Ch.

with Na_{2}CO_{3} a globule of metallic silver is obtained. The mineral frequently contains copper and iron.

~Kerargyrite~, AgCl, Ag . 75.3, Cl . 24.7.--H = 1.0-1.5, G = 5.52. Color, white, gray, yellowish, greenish to blue. l.u.s.tre, resinous, adamantine.

Soft like wax. Fuses easily in a candle-flame. Before the Bp. on Ch. it is readily reduced to metallic silver.

ORES OF TIN

~Ca.s.siterite~, SnO_{2}, Sn . 79, O . 21.--

H = 6.0-7.0, G = 6.8-7.0.

Color, brown, black. l.u.s.tre, adamantine, brilliant. Occurs crystallized in square prisms. Reentrant angles characteristic. Before the Bp. on Ch.

with Na_{2}CO_{3} and KCN reduced to a metallic globule of tin. In the borax bead gives characteristic reaction.

~Stannite~, 2 Cu_{2}S . SnS_{2} + 2 (FeS . ZnS) Sn . S_{2}.--H = 4.0, G = 4.3-4.5. Color, steel-gray to iron-black. l.u.s.tre, metallic. Occurs usually ma.s.sive and disseminated. Heated in an ignition tube it yields sulphur dioxide. Before the Bp. on Ch. it emits sulphur dioxide and becomes covered with oxide of tin. Before the Bp. on Ch. with Na_{2}CO_{3} and KCN it gives an impure globule of copper. A very difficult mineral to determine.

ORES OF ZINC

~Calamine~, H_{2}Zn_{2}O_{5}Si, SiO_{2} . 25.0, ZnO . 67.5, H_{2}O .

7.5.--H = 4.5-5.0, G = 3.4-3.5. Color, white, gray, bluish, or brown.

l.u.s.tre, vitreous. Brittle. In an ignition tube yields water when heated and becomes milky white. Before the Bp. on Ch. practically infusible.

With Co(NO_{3})_{2} it a.s.sumes a green color which pa.s.ses into a fine blue when the heat is increased.

~Smithsonite~,

Zn . CO_{3}, ZnO . 64.8, CO_{2} . 35.2.--

H = 5, G = 4.30-4.45. Color, gray, yellow, brown, and green. l.u.s.tre, vitreous, pearly. Heated in an ignition tube CO_{2} is evolved, residue appearing white. It often contains impurities of Cd, Pb, Fe, Mn, Ca, and Mg. When these are present the residue in the ignition tube becomes dark on cooling. Before the Bp. on Ch. with Na_{2}CO_{3} and exposed to the R. F. it is decomposed. It gives the characteristic reaction for zinc with Co(NO_{3})_{2}.

~Zincite~, ZnO, Zn . 80.3, O . 19.7--