70 MINERALOGY. 
granite imbedding similar crystals. The forms here represented are 
modifications and twin formations of the forms, figs. 29, 37, 42. This 
substance is a very valuable ore of tin, containing as much as 78 per cent. 
of the pure metal. In reducing the ore it is pounded fine, and roasted. By 
this means, a portion of its impurities is dissipated, especially arsenic and 
sulphur; others being converted into lighter substances which can be 
separated from the heavier tin by washing. The residuum is then to be 
heated with charcoal in the furnace, in the usual manner. The raw tin, 
thus obtained, is very impure, containing in addition lead, bismuth, arsenic, 
iron, antimony, and zinc. It is purified by the application of a gentle heat, 
during which the purer tin runs off, leaving a portion behind mixed with 
impurities. The best and purest tin is the Malacca, Banca, and English 
grain tin. After this comes the common English grain tin, then the 
English block tin, and the Bohemian and Saxony mountain tin. The 
applications of tin are very numerous. It is cast into various shapes, 
converted into different culinary utensils; covering sheets of iron plate it 
forms the material used by the tinner; mixed with mercury it constitutes 
the amalgam coating the backs of looking-glasses, &c. 
4. Rutile and Anatase. 4 
Both minerals contain the same oxyde, resembling the oxyde of tin in 
many respects. The metal obtained from them, titanium, is the only one 
of a red color besides copper. Neither mineral is abundant, the principal 
localities being Norway, Spain, France, Hungary, and Switzerland, where 
they occur in primitive rocks. Several localities in the United States are 
known where rutile is found. P/. 34, fig. 10, represents a group of rutile 
erystals drawn from nature, while figs. 28, 43, 53, give its theoretical 
forms; figs. 29 and 32 represent the crystalline form of anatase. The 
oxyde forming these minerals is an acid of titanium, called titanic acid. 
5. Pyrolusite, Braunite, Manganite, Hausmannite. 
These are all oxydes of a metal, manganese, similar in its properties to iron. 
Hausmannite is a red oxyde of manganese, and occurs crystallized, in 
shapes of jigs. 29 and 32; pyrolusite is oxyde of manganese, its crystal 
forms as in figs. 26, 28, 29; manganite is hydrated sesquioxyde of 
manganese, and crystallizes in shapes whose primary form is a rhombic 
prism (fig. 24) ; braunite is anhydrous sesquioxyde of manganese, crystallized 
like manganite, and accompanying it. Crystals of both occur together, as 
at Ilefeld, in beautiful masses, as shown from nature in fig. 7. These 
oxydes also occur amorphous, as coatings of other minerals. Pyrolusite and 
manganite are used in the manufacture of oxygen, which may be procured 
by simple heating of these minerals; their further applications in the arts 
are numerous. They are used in glass works to decolorize glass, the 
bottle-green color of common glass disappearing entirely by the addition of 
pyrolusite ; an increased proportion of the mineral produces a beautiful red 
in melted glass, which, by the addition of oxyde of tin, becomes converted 
into a flesh-color, used in the painting of porcelain and glass. The metal 
manganese has been converted to no useful purpose, owing to the difficulty 
of separating it from its ores. 
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