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Tin is a silvery white metal, with a high gloss, the relative density of 7.0, a low melting point (230 deg.] C), a hardness of 3.75, a good soft ductile. The content of tin in the earth's crust is only 2 × 10 -6 to 3 × 10 -6 . Tin-copper element group belonging to the parent, but also has an upper lithosphere amphoteric character and thiophilic affinity of oxygen. When tin and sulfur act, two compounds are formed: tin monosulfide and tin disulfide, which have strong volatility at high temperatures. Tin and oxygen can also combine to produce tin oxide and tin dioxide. Although tin has both divalent and tetravalent valence states, tetravalent compounds are more stable under natural conditions, especially tin oxide (SnO 2 ), which is one of the most stable compounds on the earth's crust.
There are more than 50 kinds of tin-containing minerals known in nature, and there are about 20 kinds of major tin minerals. At present, the main economic significance is cassiterite, followed by the yellow tin mine. Some deposits, sulfur, tin-lead ore, stibnite tin lead, tin cylinder, and sometimes sulfur black tin silver, tin boron black, Malaya stone, water cassiterite, brucite and the like may be relatively rich in tin Set, forming industrial value.
(1) The chemical composition of cassiterite is SnO 2 , Sn 78.8, O 21.2. Tetragonal crystal, the crystal is double-cone, cone-shaped, and sometimes needle-like. Often with admixtures of iron, niobium, tantalum, in addition to still containing manganese, scandium, titanium, zirconium, tungsten, and iridium, dispersed elements, and gallium. The presence of Fe 3+ often affects the magnetism, color and specific gravity of cassiterite. Xiaishi is the main source of raw materials for tin.
(2) The yellow tin ore is also known as bismuth tin ore. The chemical composition is Cu 2 FeSnS 4 , Cu 29.58, Fe 12.99, Sn 21.61, S 29.82. Tetragonal system. Crystals are rare, in the form of pseudotetrahedrons, pseudooctahedrons, and plates. Kesterite in Guangxi tin sulfide-bearing account for deposits and filling type tungsten tin deposit, Hunan high school mesothermal-type lead-zinc deposits are more common.
(3) The chemical composition of the bismuth tin ore is Pb 5 Sb 2 Sn 3 S 14 , Pb 49.71, Sb 11.64, Sn 17.04, S 21.51, and iron, zinc and the like are mixed in the composition. The crystal is thin and often curved, and the twin crystal is complicated. The aggregate is massive, radial or spherical. Produced together with bismuth lead ore and yellow tin ore, also produced in tin ore veins.
(4) The chemical composition of the sulphur-lead ore is PbSnS 2 , Pb 53.05, Sn 30.51, S 16.44. Orthorhombic system. The crystal is plate-shaped and has a shape that is nearly square. Usually a block assembly. It is often produced in tin ore veins together with cassiterite, galena, sphalerite, and pyrite.
(5) The chemical composition of the cylindrical tin ore is Pb 3 Sb 2 Sn 4 S 14 . Orthorhombic system. A cylindrical or blocky and spherical aggregate. It is produced in the tin vein together with stilbene tin ore, sphalerite and pyrite.
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