CASSITRRITE (from the Gr. Kavvirepos, tin)

This article appears in Volume V05, Page 461 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: CAR-CAU

CASSITRRITE (from the Gr. Kavvirepos, tin) , the mineralogical name for tin-stone, the common ore of tin. It consists of tin dioxide, or stannic

oxide

OXIDE

(SnO2), and crystallizes in the tetragonal 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 figs. 2 and 3, are common. Certain slender prismatic crystals, with an acute 8-sided pyramid, are known in

Cornwall

CORNWALL

as " spar-able tin," in allusion to their resemblance to sparable nails, whilst very slender crystals are termed needle-tin. Occasionally the

mineral

MINERAL

occurs in fibrous forms, which pass under the name of
"

wood

-tin," and these, though not unknown in the 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 sand, and is then known as stream tin or alluvial tin. This detrital tin-ore was probably used as a source of the metal before the primitive miners had learnt to attack the solid tin-bearing rocks.
Pure cassiterite may be colourless, or
white, as seen in certain specimens from
the Malay Peninsula; but usually the

mineral

MINERAL

is brown or even black, the
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 contour of the crystal. A brown
variety, with rather resinous lustre, is termed " rosin tin."
The usual lustre of crystals of cassiterite is remarkably splendent,
even adamantine. The mineral has a high refractive index,
and strong bi-refringence. Certain transparent yellow and brown
specimens, cut as gem-stones, exhibit considerable brilliancy.
The hardness of cassiterite is 6.5, so that it cannot be scratched with a knife, and is nearly as hard as quartz. Its specific gravity is about 7; and in consequence of this high density, the tin-stone is readily separated during the process of dressing, from all the associated minerals, except wolframite, which may, however, be removed by magnetic separators.
Cassiterite usually occurs as veins or impregnations in granitic rocks, and is especially associated with the quartz-mica rock called greisen. The usual associates of the tin-stone are quartz, tourmaline, apatite, topaz, beryl, fluorite, lithia-mica, wolframite, chalcopyrite, &c. The presence of fluorine in many of these minerals has led to the

opinion

OPINION (Lat. opinio, from opinari, to think)

that the tin has been derived in many cases from an acid or granitic magma by the action of fluorine-bearing vapours, and that cassiterite may have been formed by the interaction of tin fluoride and water vapour. Cassiterite occurs as a pseudomorph after orthoclase felspar in some of the altered granite of

Cornwall

CORNWALL

, and it has occasionally been found as a cementing material in certain brecciated lodes.
Among the localities yielding cassiterite may be mentioned Cornwall, Saxony, Bohemia, Brittany, Galicia in Spain; the Malay peninsula, and the islands of Banca and Billiton; New South Wales, Queensland and Tasmania. Fine examples of

wood

-tin, occurring with topaz, are found in Durango in

Mexico

. Deposits of cassiterite under rather exceptional conditions are worked on a large scale in Bolivia; and it is notable that cassiterite is found in Liassic limestone near Campiglia Marittima in Tuscany. Cassiterite has been worked in the

York

region, Alaska. (F. W. R.*)

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

If you wish, you can link directly to this article.

<a href="http://jcsm.org/StudyCenter/Encyclopedia/CAR_CAU/CASSITRRITE_from_the_Gr_Kavvir.html">
CASSITRRITE (from the Gr. Kavvirepos, tin)
</a>

(Previous)
CASSITERIDES (from the Gr. Kavo-irepos, tin, i....

(Next)
CASSIUS

JCSM was founded in 1997 and exists to help the community and bring people into a life-changing and productive relationship with Jesus Christ. JCSM offers over 200,000 free web pages, including its weekly inspirational emails that were sent continuously for over a decade.

Jesus Christ Saves Ministries
P.O. Box 9297
San Diego, CA 92169
1-888-887-0417 or Email