KAJ R. SVENSSON / SCIENCE PHOTO LIBRARY KAJ R. SVENSSON / SCIENCE PHOTO LIBRARY
Quartz crystal. View of a crystal of smoky quartz showing small tourmaline inclusions (dark needles). Quartz (silicon oxide) is colourless when pure, but the presence of impurities can give a range of colours including white, pink, yellow, blue, green, violet and smoky brown, as here. Tourmaline is a complex borosilicate mineral which may also occur in varying colours, sometimes differing even in the same crystal.
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