Cassiterite
| Cassiterite | |
|---|---|
Image:CassiteriteUSGOV.jpg Botryoidal Cassiterite | |
| General | |
| Category | Mineral |
| Chemical formula | SnO2 |
| Identification | |
| Colour | black or 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 |
| Refractive index | Nearly transparent to opaque |
| Pleochroism | None |
| Streak | White to brownish |
| Specific gravity | 6.4 - 7.1 |
| Fusibility | infusible |
| Solubility | insoluble |
| 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.
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.
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.
Cassiterite has recently become an illegally mined and traded mineral in Democratic_Republic_of_the_Congo. This is due to great increase in tin demand because new lead-free solder materials have a larger proportion of tin. It is generally traded by same organisations as coltan.
References
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York, pp 306-307 ISBN 0471805807
- Mineral galleries accessed 4-21-05
- Mindat accessed 4-21-05
- Webmineral accessed 4-21-05
- Australian source accessed 4-21-05
- ReliefWeb accessed 7-20-05de:Zinnstein