G
= 5.77-5.86. Color, black to dark cochineal-red. Lustre, 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.

~Proustite~, 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. Lustre, splendent, adamantine. Before
the Bp. on Ch. it behaves like pyrargyrite, save that it gives off
arsenical 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. Lustre, 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. Lustre, 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

~Cassiterite~, SnO_{2}, Sn . 79, O . 21.--

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

Color, brown, black. Lustre, 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. Lustre, metallic. Occurs
usually massive 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.
Lustre, 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 assumes a green color which passes into a fine