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Cassiterite Mineral Facts:

Chemical Formula: SnO₂

Colors: Normally Brownish red to black
By transmitted light, the mineral is brown or black. Its luster is very brilliant, and its streak is white, gray or brown, rarely yellow or colorless. The purest specimens are nearly transparent, though the ordinary varieties are opaque. Streak. White or pale grey to brownish.

Hardness: 6.5

Density: 7

Cleavage: Imperfect cleavage parallel to  P(100) and P(111). Fracture Subconchoidal, or uneven; brittle.

Crystallography: Tetragonal
Tetragonal prisms terminated by tetragonal pyramids ; crystals often twinned. Also occurs massive, and sometimes disseminated in small grains; also fibrous..

Luster:. Adamantine luster on crystals, usually very brilliant. . Transparent to translucent.

Optics: (Refractive Index):  w= 3.0877, e= 2.7924

Composition, Structure and Associated Minerals:
Cassiterite, or tinstone, is the only worked ore of tin. It is obtained from both lodes and alluvial (placer) deposits. In the former it may be associated with arsenic, copper and iron pyrites, wolfram, etc., and in alluvial deposits it occurs as rolled pebbles of a dark brown color in the beds of streams, as fibrous aggregates, and as glistening black crystals often associated with ilmenite or titaniferous iron, monazite, zircon, topaz, tourmaline, etc.  derived from the same veins. Fully one half of the world's supply of tin is obtained from placer deposits, resulting from the degradation of tin bearing veins.

Cassiterite occurs in hydrothermal veins, associated with acid rocks, granites, as in Cornwall. The main occurrence of cassiterite is in quartz veins, associated with fluorite, topaz, tourmaline, axinite, and apatite, as in Cornwall, Saxony, and Bolivia.Tin veins are usually rich in boron or fluorine, and contain minerals like tourmaline, topaz, fluorite and apatite. Wood Tin is a variety of cassiterite, in which the structure is compact and fibrous internally, exhibiting concentric bands, which cause it somewhat to resemble wood; it occurs in reniform masses.

Identification and Diagnostics
Cassiterite is only slightly acted upon by acids. It may be reduced to a metallic globule of tin only with difficulty, even when mixed with sodium carbonate and heated intensely on charcoal. The mineral is most easily distinguished from other compounds that resemble it in appearance by its high density and its inertness when treated with reagents or before the blowpipe.

Occurrence, Localities and Origins:
The crystallized mineral occurs at many places in Bohemia and in Saxony, at Limoges in France and sparingly in a few places in the United States, especially near El Paso, Texas, in Cherokee Co., N. C., in Lincoln Co., S. C., and near Hill City, S. D.

Localities of alluvial tin deposits are Malaysia; Bolivia; Indonesia,  Russia; Cornwall; Mount Bischoff, in Tasmania, Thailand, China, etc.  Massive tinstone and stream tin occur in large enough quantities to be mined in Cornwall, England; on the Malaysian Peninsula and on the islands lying off its extremity; in Tasmania; in New South Wales, Victoria and Queensland, Australia; in the gold regions of Bolivia; at Durango in Mexico, and at various points in Alaska, at some of which there are 400 lb. of cassiterite in a cubic yard of gravel.

Use. Cassiterite is the only important ore of tin. Tin is also used in various alloys: solder, containing tin and lead; bell-metal and bronze, containing copper and tin.

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