Tin has been known since early Roman times, and the mines at Cornwall, England, were worked from that time all through down to the present, but now they are becoming of minor importance as they approach exhaustion. The metal is silvery-white, does not easily tarnish, is malleable, but has little ductility and little tensile strength. Tin is mostly used in making tin plate, a thin sheet of steel covered with tin, the tin being only 1 to 2% of the total weight. This tin plate is mostly made into tin cans, and used as containers for food. Some tin is used in making solder, tin-foil, tubes for paste, vaseline, etc., and around 1000 tons per year for weighting silk. This “weighting” makes the silk heavier by about 25% and gives it a “rustle,” which, while much in evidence, is really indicative that the silk is not pure. The United States produces very little tin, most of the world’s supply coming from the Malay Peninsula, Dutch East Indies, China, and Bolivia, with small amounts from several other countries.
[Cassiterite]
SnO₂
[Pl. 28]
tin stone
Occurs in tetragonal crystals, massive, or in grains and pebbles; hardness 6.5; specific gravity 7; color black or dark-brown; streak gray; luster adamantine; translucent on thin edges.
The crystals are short prisms with pyramidal ends. Twinning is common. Cassiterite also occurs in fibrous masses, and when it is weathered from its original location, is so insoluble and hard, that it remains as grains and pebbles, making placer-deposits, from which today three quarters of the supply is obtained. If pure, the crystals would be colorless, but impurities of iron and titanium give it the dark-brown to black color. Cassiterite may appear very like rutile, the crystalline forms being identical, but the reddish tinge of color in the rutile will separate the two.
Cassiterite is one of those minerals which result from deposition at very high temperatures, probably from vapors, and is found in the veins in igneous rocks, such as light-colored granites, gneisses, syenites, etc. While not mined in this country it is found in small quantities in Maine, Massachusetts, New Hampshire, Virginia, Alabama, Wyoming, Montana, and California.
Titanium
Titanium, as a metal, is a heavy, gray, iron-like powder, which is chiefly useful as an alloy with iron, giving it toughness, and preventing bubbles and cracks in casting. It is not as rare as some other metals which have found a wider use.
[Rutile]
TiO₂
[Pl. 28]
Occurs in tetragonal crystals, and in grains; hardness 6.5; specific gravity 4.2; color red to reddish-brown; streak yellowish-brown; luster metallic to adamantine; translucent on thin edges.
Rutile usually occurs in crystals, which are either short and stout, or in needle-like crystals. Twinning is common. In form and general appearance it resembles cassiterite, but the reddish color, and the yellowish-brown streak will distinguish the rutile. It is found in similar rocks, granites, gneisses, syenites, and mica-schists, the two minerals cassiterite and rutile often occurring together. This is also true of the grains, which have been weathered out and are found in sands and gravels of placer deposits. It is found in small quantities in all the New England States, New York, and all down the Appalachian Mountains, especially at Graves Mountain, Ga., and in Arkansas and Alaska.