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Cassiterite

Cassiterite, 80mm plate of cassiterite and quartz crystals
General
Category Mineral
Chemical formula SnO2
Identification
Color purple, wine, black, reddish brown or yellow
Crystal habit Pyramidic, prismatic
Crystal system tetragonal; 4/m 2/m 2/m
Cleavage good in two directions forming prisms, poor in a third (basal)
Fracture Subconchoidal to rough
Mohs scale hardness 6 - 7
Luster adamantine or greasy
Streak White to brownish
Specific gravity 6.4 - 7.1
Pleochroism None
Fusibility infusible
Solubility insoluble
Other characteristics 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. Fighting over cassiterite deposits (particularly in Walikale) is a major cause of the conflict waged in eastern parts of the Democratic Republic of the Congo.[1][2]

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. Cassiterite has also been located by Seminole Group Colombia in the Amazons of Colombia, South America. The quality of the ore found had an analysis of over 72% Sn02.

Crystallography

crystal structure of cassiterite

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.

Close up of cassiterite crystals

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.
  • Mineral galleries accessed 4-21-05.
  • Mindat accessed 4-21-05.
  • Webmineral accessed 4-21-05.
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1911 encyclopedia

Up to date as of January 14, 2010
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From LoveToKnow 1911

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Simple English

Cassiterite is a mineral. Its chemical formula is SnO2. It contains tin dioxide. It is black because of impurities. It is the main ore of tin. Its Mohs hardness is 6-7.


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