Industrial Archaeological Features Industrial activity finds its most striking manifestation in a very fine example of medieval and later tin working. It takes the form of an openwork over one km. long from east to west and up to 250m. wide (L). The worked area has scarped sides up to 6m. deep and it is filled with tinners’ shafts, trial pits, and waste heaps (not depicted in detail on this overlay). The west end of the openwork runs into Lower Hooksbury Wood, where it is not visible on air photographs. It is served by numerous leats running in from north and south and the actual remains of some mining buildings appear to survive in places, particularly at Wheal Florence (M) where the remains of a whim platform can also be recorded. A very unusual alignment of pits (N), presumably derives from mineral prospecting but their date and specific function are unknown.
Cassiterite, also called tinstone, heavy, metallic, hard tin dioxide (SnO2) that is the major ore of tin. It is colourless when pure, but brown or black when iron impurities are present. Commercially important quantities occur in placer deposits, but cassiterite also occurs in granite and pegmatites. Early in the 15th century, the cassiterite veins in Saxony and Bohemia were mined for tin; peak production occurred there in the 17th century. In the 18th and much of the 19th centuries, the very large vein deposits of Cornwall were the major source of tin. Today most of the world’s cassiterite is mined in Malaysia, Indonesia, Bolivia, Nigeria, Myanmar (Burma), Thailand, and parts of China; other countries produce smaller amounts. For detailed physical properties, see oxide mineral (table).
