Cassiterite

Cassiterite

Infobox mineral
name = Cassiterite
category =
boxwidth =
boxbgcolor =


imagesize =
caption = Cassiterite crystals
formula = SnO2
molweight =
color = purple, wine, black, reddish brown or yellow
habit = Pyramidic, prismatic
system = tetragonal; 4/m 2/m 2/m
twinning =
cleavage = good in two directions forming prisms, poor in a third (basal)
fracture = Subconchoidal to rough
mohs = 6 - 7
luster = adamantine or greasy
refractive =
opticalprop =
birefringence =
pleochroism = None
streak = White to brownish
gravity = 6.4 - 7.1
density =
melt =
fusibility = infusible
diagnostic =
solubility = insoluble
diaphaneity =
other = high refractive index of approximately 2.0

Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite is the chief ore of tin today.

Occurrence

Most sources of cassiterite today are found in alluvial or placer deposits containing the resistant weathered grains. The best source of primary cassiterite is the tin mines of Bolivia, where it is found in hydrothermal veins. Cassiterite is a widespread minor constituent of igneous rocks. The Bolivia veins and the old exhausted workings of Cornwall, England, are concentrated in high temperature quartz veins and pegmatites associated with granitic intrusives. The veins commonly contain tourmaline, topaz, fluorite, apatite, wolframite, molybdenite, and arsenopyrite. The current major tin production comes from placer or alluvial deposits in Malaysia, Thailand, Indonesia, and Russia. Hydraulic mining methods are used to concentrate the fine particles of ore.

Crystallography

Crystal twinning is common in cassiterite and most aggregate specimens show crystal twins. The typical twin is bent at a near-60-degree angle, forming an "Elbow Twin". Botryoidal or reniform cassiterite is called "wood tin".

Cassiterite is also used as a gemstone and collector specimens when quality crystals can be found.

The name derives from the Greek "kassiteros" for "tin" - or - from the Phoenician word "Cassiterid" referring to the islands of Ireland and Britain, the ancient sources of tin - or - as Roman Ghirshman (1954) suggests, from the region of the Kassites, an ancient people in west and central Iran.

References

*Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York, pp 306-307 ISBN 0-471-80580-7
* [http://mineral.galleries.com/minerals/oxides/cassiter/cassiter.htm Mineral galleries] accessed 4-21-05
* [http://www.mindat.org/min-917.html Mindat] accessed 4-21-05
* [http://webmineral.com/data/Cassiterite.shtml Webmineral] accessed 4-21-05


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