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CASSITRRITE (from the Gr. Kavvirepos,...

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Originally appearing in Volume V05, Page 461 of the 1911 Encyclopedia Britannica.
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CASSITRRITE (from the Gr. Kavvirepos, See also:tin) , the mineralogical name for tin-See also:stone, the See also:common ore of tin. It consists of tin dioxide, or stannic See also:oxide (SnO2), and crystallizes in the tetragonal See also:system. The crystals are usually 4-sided or 8-sided prisms, striated vertically, and terminated by pyramids (fig. I). Twins, with characteristic re-entrant angles, such as See also:figs. 2 and 3, are common. Certain slender prismatic crystals, with an acute 8-sided See also:pyramid, are known in See also:Cornwall as " spar-able tin," in allusion to their resemblance to sparable nails, whilst very slender crystals are termed See also:needle-tin. Occasionally the See also:mineral occurs in fibrous forms, which pass under the name of " See also:wood-tin," and these, though not unknown in the See also:matrix, are generally found as rolled pebbles. By the disintegration of tin-bearing rocks and vein-stones, the cassiterite passes into the beds of streams as rolled fragments and grains, or even See also:sand, and is then known as stream tin or alluvial tin. This detrital tin-ore was probably used as a source of the See also:metal before the See also:primitive miners had learnt to attack the solid tin-bearing rocks. Pure cassiterite may be colourless, or See also:white, as seen in certain specimens from the See also:Malay See also:Peninsula; but usually the mineral is See also:brown or even See also:black, the See also:colour being referred to the presence of other impurity.

Occasionally the tin-stone is red. In microscopic sections the colour is often seen to be dis- posed in zones, following the See also:

contour of the crystal. A brown variety, with rather resinous lustre, is termed " See also:rosin tin." The usual lustre of crystals of cassiterite is remarkably splendent, even adamantine. The mineral has a high refractive See also:index, and strong bi-refringence. Certain transparent yellow and brown specimens, cut as See also:gem-stones, exhibit considerable brilliancy. The hardness of cassiterite is 6.5, so that it cannot be scratched with a See also:knife, and is nearly as hard as See also:quartz. Its specific gravity is about 7; and in consequence of this high See also:density, the tin-stone is readily separated during the See also:process of dressing, from all the associated minerals, except See also:wolframite, which may, however, be removed by magnetic separators. Cassiterite usually occurs as See also:veins or impregnations in granitic rocks, and is especially associated with the quartz-See also:mica See also:rock called See also:greisen. The usual associates of the tin-stone are quartz, See also:tourmaline, See also:apatite, See also:topaz, See also:beryl, fluorite, lithia-mica, wolframite, chalcopyrite, &c. The presence of See also:fluorine in many of these minerals has led to the See also:opinion that the tin has been derived in many cases from an See also:acid or granitic magma by the See also:action of fluorine-bearing vapours, and that cassiterite may have been formed by the interaction of tin fluoride and See also:water vapour. Cassiterite occurs as a pseudomorph after See also:orthoclase See also:felspar in some of the altered See also:granite of Cornwall, and it has occasionally been found as a cementing material in certain brecciated lodes. Among the localities yielding cassiterite may be mentioned Cornwall, See also:Saxony, Bohemia, See also:Brittany, See also:Galicia in See also:Spain; the Malay peninsula, and the islands of Banca and See also:Billiton; New See also:South See also:Wales, See also:Queensland and See also:Tasmania.

See also:

Fine examples of wood-tin, occurring with topaz, are found in See also:Durango in See also:Mexico. Deposits of cassiterite under rather exceptional conditions are worked on a large See also:scale in See also:Bolivia; and it is notable that cassiterite is found in Liassic See also:limestone near Campiglia Marittima in See also:Tuscany. Cassiterite has been worked in the See also:York region, See also:Alaska. (F. W.

End of Article: CASSITRRITE (from the Gr. Kavvirepos, tin)

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