MARTIN LAND / SCIENCE PHOTO LIBRARY MARTIN LAND / SCIENCE PHOTO LIBRARY
A sample of smithsonite, a useful source of zinc, found at Tsumeb in Namibia. Pure smithsonite (zinc carbonate) is white, as here. The presence of copper impurities turns the mineral green/blue, while traces of cadmium result in a bright yellow colour. Smithsonite is a typical sedimentary precipitate produced by the action of waters rich in zinc sulphate on carbonate rocks. This mineral was named in honour of James Smithson, after whom the Smithsonian Institute was founded.
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