|
|
www.mineralgallery.co.za Minerals A-E |
|
|
Cassiterite |
||
Name
Cassiterite
Chemistry
SnO2 Tin oxide. Sn = 78.6 %. O = 21.4 %. Iron may substitute for tin up to about 1.6% and tantalum and niobium are often present in small amounts.
Uses
a source of tin.
Color
Reddish brown to brownish black, but raraely colorless or yellow.
Hardness
6-7
Specific gravity
6.99
Crystal system:
Tertagonal; ditetragonal dipyramidal. Crystals usually short prismatic or with acute terminations; sometimes long prismatic or with acute terminations. Also massive, in radially fibrous crust or concretionary masses; and granular.
Accompanied by:
Tantalum and niobium
Fracture
Subconchoidal or uneven.
Luster
Adamantine to splendent, sometimes tending to be greasy on fracture surfaces
Cleavage
(100) imperfect
Streak
White, greyish or brownish.
Similar to:
Rutile, wolfram, garnet, ilmenite, sphalerit.
Cassiterite is distiguished by its high specific gravity and by its color and hardness. It is virtually infusible before the blowpipe.
The best and simplest test is to place a grain in contact with zinc in cold dilute hydrocloric or sulpheric acid(not nitric) when the nascent hydrogen produced will reduce the oxide to metallic tin. The resulting metal-coated can be polished to yeild an unmistakable bright silver-white surface.
The minerals commonly mistaken for cassiterite rutile and sphalerite.
In reducing blowpipe flame cassiterite can also be reduced to tin on charcoal, preferably with sodium carbonate. Insoluble in acids.
Cassiterite is practiclly the only ore-mineral of tin. A small amount is extracted from tin sulphide minerals. Black tin is a trade term used for dressed tin ore (with about 70 percent metallic tin).
