H = 2.0-2.5, G = 7.20-7.36.
Color, blackish lead-gray. Lustre, 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, Ag3SbS3, Ag . 59.8, Sb . 22.5, S . 17.7.—H = 2.5, 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 Na2CO3 is reduced to metallic silver.
Proustite, Ag3S3As, 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, Ag5S4Sb, 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 Na2CO3 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, SnO2, 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. Reëntrant angles characteristic. Before the Bp. on Ch. with Na2CO3 and KCN reduced to a metallic globule of tin. In the borax bead gives characteristic reaction.