Images
Formula: SnO2
Simple oxide, rutile group
Specific gravity: 6.98 to 7.01
Hardness: 6 to 7
Streak: Brownish white, white, greyish
Colour: Black, yellow, brown, red or white.
Solubility: Slightly soluble in hydrochloric and nitric acid; insoluble in sulphuric acid
Environments:
Plutonic igneous environments
Pegmatites
Placer deposits
Hydrothermal environments
Cassiterite is widely distributed. It occurs as a primary mineral
in igneous
rocks and
pegmatites but it is more commonly found as an unaltered
primary mineral in
hypothermal (high temperature) hydrothermal quartz veins of tin deposits in
or near
granitic rocks. Because of its durability it is also found frequently in
placer deposits.
In high temperature quartz veins associated with granitic intrusions cassiterite
is often
associated with
ferberite,
molybdenite and
arsenopyrite.
Localities
At Llallague, Bolivia, cassiterite in hydrothermal veins crystallises at about 300oC
(Mineralogy and Petrology 111.547-568).
The Needle Hill Mine, Needle Hill, Sha Tin District, New Territories, Hong Kong, China, is a tungsten mine, abandoned
in 1967. The principal ore is wolframite, and the principal gangue mineral is
quartz. Molybdenum also occurs. The
mineralisation consists of a series of parallel fissure veins that cut through
granite. Wolframite and
quartz are the main minerals, but galena,
sphalerite, pyrite,
molybdenite and fluorite have also
been found here
(Geological Society of Hong Kong Newsletter 9.3.29-40).
The quartz-wolframite veins are of
high-temperature hydrothermal formation,
and grade into wolframite-bearing
pegmatites.
Wolframite is almost always associated with molybdenite. Other
associated minerals found occasionally include pyrite,
chalcopyrite, arsenopyrite,
sphalerite, bismuth,
fluorite, topaz and cassiterite
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
At Wheal Coates, St Agnes, Cornwall, Engand, UK, a cassiterite pseudomorph
after a Carlsbad twin of orthoclase has been found
(KL p141).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, cassiterite has been found as crystals to several centimetres
and as masses to 60 cms. Sometimes it is found in intimate intergrowth with columbite
group species. The Emmons pegmatite is an example of a highly evolved
boron-lithium-cesium-tantalum
enriched pegmatite
(R&M 94.6.505-506).
Common impurities: Fe,Ta,Nb,Zn,W,Mn,Sc,Ge,In,Ga
Back to Minerals