Cassiterite

Cassiterite, oxide of tin or common tin ore, occurs massive or in the form of crystals, which are often quadrangular prisms terminated by four-sided pyramids. It appears, however, in many other complex crystalline forms. These are gener- ally blackish brown or black, but greenish shades are also met with—the dark varieties being opaque, while those that are lighter in colour are somewhat translucent. Cassiterite contains about 78 per cent. of tin, and is the ore from which most of the tin of commerce is obtained. It has been worked from a very remote period in Cornwall, and is met with in many other countries, as in Brittany, Bohemia, Saxony, Spain, Finland, Sweden, Greenland, United States, California, Mexico, Chili, Sumatra, &c. Stream tin is the name given to rounded fragments of cassiterite which occur in alluvial deposits in the valleys of Cornwall, &c.