Some Nuggets about Zinc

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Wendy Kirk

The body of the car is said to be made from zinc. Is zinc poisonous? Where does it come from?
Zinc is generally thought to be non-toxic, although the metal may be a human skin irritant. It is certainly an essential element for humans; nonetheless, too much zinc can lead to vomiting, stomach cramps, diarrhoea and fever. Cases if mass poisoning are said to have occurred where fruit juice has been stored in galvanized containers. But it seems unlikely that the zinc caused the child’s problems. There is in fact a plant which just LOVES zinc. This is a variety of Viola calaminaria (Yellow zinc violet) which grows on old zinc mines in Central Europe.
What are the most important ores of zinc? Sphalerite for one, whose name comes from the Greek sphaleros meaning treacherous. Nothing to do with health, but the fact that is was often mistaken for the lead sulphide mineral galena, with which it is often associated. Sphalerite itself is usually black or brown, with a lustre like resin, or even brilliant. The powdered mineral is pale yellow or brown, a good identifying characteristic, and it has cubic crystals. Examples can be found in the UCL Geology Collections. Sphalerite tends to form in hydrothermal vein deposits and in skarns. Extraction of zinc from sphalerite involves roasting the ore to form the oxide, followed by reduction in a furnace in the presence of coke, in an inert atmosphere. Alternatively, the oxide is converted to zinc sulphate and then the zinc extracted electrolytically. Zinc is used mostly as sheets for galvanising iron, but is also alloyed with copper to make brass. As of 2003, world production was around 7 million tonnes per annum, and the main producers are USA, Canada, Australia, Russia and Peru.
Another ore mineral is smithsonite, which is zinc carbonate. This can be a variety of colours, and is a very attractive mineral – again, there are a number of specimens in the Geology Collections, and some are on display in the first floor corridor of South Wing. These were donated in 1912 to UCL by Dr Henry Johnston-Lavis, and were collected from the lead-zinc mines of Lourion, Greece, an area where minerals have been seriously over-collected, so these are rather special. Smithsonite was named after James Smithson, a British geologist, who left his fortune to found the Smithsonian Institute in Washington. Smithsonite is a secondary mineral, forming in the weathered zone of zinc deposits, and sometimes replacing adjacent carbonate rocks. Today it is found in Namibia, Zambia and in Mausbach in western Germany.
References can be provided on request ……………….